GitLab

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