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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Standardize filter bar layout across admin pages to place search/filters
on left and action buttons on right within the same row, improving
visual consistency and space utilization.

Implements announcements end-to-end (admin CRUD + read status, user list + mark read) with OR-of-AND targeting. Also breaks the ent<->service import cycle by moving schema-facing constants/targeting into a new domain package.