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- Sidebar user-side order: /available-channels now sits directly above
  /monitor (渠道状态) for regular users, mirroring the admin section where
  it sits above /admin/channels.
- GroupBadge gains an alwaysShowRate prop. Subscription groups default to
  a "订阅"/days-remaining label; the new flag swaps that for the rate
  multiplier while keeping the subscription theme color, so the Available
  Channels page can surface rates on every group type.

Pricing popover:
- Teleport to body + fixed-position re-measuring on hover/scroll/resize so it
  escapes the card's overflow-hidden clip that was chopping off the lower
  half of the panel.
- Header + border adopt the platform theme via platformBorderClass /
  platformBadgeLightClass so each model card reads at a glance.

Accessible groups:
- Backend AvailableGroupRef / user DTO now expose subscription_type,
  rate_multiplier and is_exclusive. User-specific rates continue to come
  from /groups/rates (same pattern as the API keys page).
- Table renders groups through the shared GroupBadge, which already deepens
  subscription-type colors and shows default vs custom rate as
  <s>default</s> <b>custom</b>.
- Exclusive groups are labelled with a purple shield row, public groups
  with a grey globe row so admins and users can tell at a glance which
  groups they got via explicit grant vs. public access.

i18n keys for exclusive / public / their tooltips added to zh + en.

Switch the user-facing 'Available Channels' view from "one row per
platform" to "one channel row-group with N platform sections".

Backend: userAvailableChannel now holds Platforms []section instead
of being exploded. buildPlatformSections replaces
explodeChannelByPlatform with the same per-platform grouping logic.

Frontend: drop the DataTable wrapper for this view and write a
four-column grid table (渠道名 / 平台 / 分组 / 支持模型) where the
channel name only renders on the first platform row of each channel —
visual rowspan without hacking DataTable.

- api/channels.ts: UserChannelPlatformSection + platforms[]
- AvailableChannelsTable: rewritten as native grid (header + per-
  channel section with hover row highlight)
- AvailableChannelsView: search now filters platforms sub-array;
  channel-name / description hits still keep the whole channel
- i18n: add availableChannels.columns.platform (zh/en)

Backend: one source channel → N output rows, one per platform that
has user-visible groups. Each row carries a single platform, so the
frontend can color/icon an entire row without mixing sources.

- userAvailableChannel: add Platform field
- new explodeChannelByPlatform helper; drop now-redundant
  collectGroupPlatforms

Frontend: use the row platform to drive theming and stop repeating
"ANTHROPIC" / "OPENAI" labels on every model chip.

- api/channels.ts: UserAvailableChannel.platform
- AvailableChannelsTable: name cell — PlatformBadge next to channel
  name (replaces the two-line name/description block; description
  moves to the badge's title tooltip); groups cell — each chip uses
  platformBadgeLightClass + PlatformIcon; model list passes
  show-platform=false + platform-hint to child chips
- SupportedModelChip: chip bg/border driven by platformBadgeClass,
  leading PlatformIcon; platform-hint fallback when model.platform
  missing

- channel.go: convert normalizeBillingModelSource into a (*Channel) method for entity cohesion
- channel_service.go: normalize in populateChannelCache so every cache-backed reader (gateway, billing, future endpoints) sees the default; drop the duplicate fallback inside resolveMapping
- table: tighten Row with status?: ChannelStatus / billing_model_source?: BillingModelSource, remove the [key: string]: unknown index signature
- admin view: drop the `as ChannelStatus` / `as BillingModelSource` assertions and add statusStyleOf / billingSourceLabelOf helpers with runtime fallback so unseen values render as "-" instead of crashing

- service: add normalizeBillingModelSource helper, apply in Create/GetByID/Update/List/ListAvailable outputs
- handler: drop channelToResponse fallback now that service owns the default; add passthrough test
- frontend: replace ternary status/billing-source lookups with Record<Enum, ...> maps so new union members fail the build
- chip/table: drop local type aliases, reuse UserSupportedModel/UserPricingInterval directly
- tests: assert short-circuit on ListAll error, wrap-prefix preservation, and Name-based default lookup

- service: drop groupRepo nil guard (DI must inject), switch SupportedModels to SliceStable to match doc
- frontend: reuse user-side DTO types in SupportedModelChip/AvailableChannelsTable instead of duplicating shapes; narrow admin statusLabel param to ChannelStatus
- tests: replace nil-groupRepo case with ListAll/ListActive error propagation and BillingModelSource default-backfill coverage

Follow-up to the available-channels review pass. No behavior change for
end users; tightens internals based on three independent code reviews.

Backend
- service/channel.go: collapse buildPricingLookup + pricedNamesFor
  into a single platformPricingIndex (byLower + originalCase + ordered
  names), built once per SupportedModels call. Fixes a casing-
  consistency bug where the same logical model appeared with mapping
  case in the exact branch but pricing case in the wildcard branch —
  pricing's original case now wins everywhere.
- service/channel.go: doc that a mapping key of just "*" expands to
  every priced model on the platform (intentional "passthrough all").
- service/channel_available.go: normalize empty BillingModelSource to
  channel_mapped at construction time, removing the same fallback
  duplicated in the admin DTO mapper and the admin Vue template.
- handler/admin/available_channel_handler.go: unexport
  availableChannelToAdminResponse (same-package usage only); mapper
  is now a pure passthrough.
- handler/available_channel_handler.go: drop the middleware2 alias
  (no name collision in this file).

Frontend
- utils/pricing.ts: extract formatScaled, used by SupportedModelChip
  and PricingRow.
- api/admin/channels.ts: re-export BillingMode from constants/channel;
  tighten Channel.status / billing_model_source to ChannelStatus /
  BillingModelSource (and same for AvailableChannel).
- components/channels/AvailableChannelsTable.vue: drop dead
  withDefaults wrapper (loading is required, both call sites pass it).
- views/admin/AvailableChannelsView.vue: drop the redundant
  || BILLING_MODEL_SOURCE_CHANNEL_MAPPED fallback (now applied in
  service layer); remove unused import.
- i18n zh + en: delete unused tierLabel and tokenRange keys from
  both availableChannels.pricing and admin.availableChannels.pricing.

Tests
- New: SupportedModels_ExactKeyUsesPricedCaseWhenAvailable locks the
  pricing-case-wins rule.
- New: SupportedModels_AsteriskOnlyMappingExpandsAllPriced documents
  the "*" expansion rule.
- Admin handler: existing tests adjusted to pass an explicit
  BillingModelSource (default-fill is now exercised by service tests).

Add a read-only aggregate view per channel: its linked groups and a
deterministic wildcard-free supported-model list with pricing details.

Backend
- service.Channel.SupportedModels(): combine ModelMapping keys with
  same-platform ModelPricing.Models; trailing "*" keys expand via
  pricing prefix match; platforms without a mapping produce no
  entries (intentional "no mapping = not shown" rule).
- Extract splitWildcardSuffix() shared with toModelEntry.
- Build a per-call pricing lookup map (platform+lowerName -> *pricing)
  to avoid O(N*M) scans in SupportedModels.
- ChannelService.ListAvailable() aggregates channels + active groups;
  filters out group IDs no longer active.
- Admin route GET /api/v1/admin/channels/available returns the full
  DTO (id, status, billing_model_source, restrict_models, groups,
  supported_models).
- User route GET /api/v1/channels/available applies three filters:
  Status==active, visible-group intersection, and platform filter
  on supported_models (prevents cross-platform leak when a channel
  links to both a user-accessible group and an inaccessible one on
  another platform). Response is a plain array (matches the
  /groups/available sibling shape). Field whitelist omits
  billing_model_source, restrict_models, ids, status, sort_order.

Frontend
- New /admin/available-channels and /available-channels views backed
  by a shared AvailableChannelsTable component (admin adds status +
  billing-source columns via slots).
- PricingRow extracted to its own SFC; SupportedModelChip references
  shared billing-mode constants in constants/channel.ts.
- Sidebar: new entry above "渠道管理" for admin; matching entry in
  user nav.
- i18n: zh + en coverage for both namespaces.

Tests
- SupportedModels: wildcard-only pricing skipped, prefix-matches-
  nothing, cross-platform bleed, case-insensitive dedup, empty
  platform mapping.
- ListAvailable: nil groupRepo, inactive-group-ID dropped, stable
  case-insensitive name sort.
- User handler: 401 on unauthenticated, visible-group intersection,
  platform filter on supported_models, JSON whitelist.
- Admin handler: full DTO including default BillingModelSource
  fallback.

Refs: issue #1729