v1.28.0

Added

• AdminNotice dataclass and admin_notices hookspec in
  bragi.api / bragi.hookspecs. Plugins return per-site
  operator-attention notices; bragi renders them on the per-site
  dashboard (full cards), the sticky rail on per-site admin pages
  (action_required + status), and the global admin index (per-site
  severity dots). Stability-contract docstring + a contract
  regression test land alongside the surface.
• bragi.contrib.admin_notices plugin: dismiss + snooze admin
  routes backed by admin_notice_dismissals, the three shared
  templates (_notice_card.html, _notice_rail.html,
  _notice_dots.html), admin_notices.css, and the in-tree
  welcome_fallback hookimpl (migrated from bragi.contrib.sites).
• bragi.api.invalidate_admin_notices(site) escape hatch for
  plugins that resolve an action_required notice via a known
  admin action (e.g. a theme calling it after a state change).
• Per-(plugin, site, generation) LRU notice cache with 30s TTL,
  explicit invalidation, and per-worker semantics matching the
  established bragi_theme_zelda.rom.cache pattern.

Changed

• bragi.contrib.sites's site dashboard renders notices through
  collect_notices instead of the previous inline
  home_status == 'welcome_fallback' banner. The replacement is
  also a small UX upgrade: same title and body text, but rendered
  as a card with a dedicated "Site settings →" CTA button and
  dismissible=False so an editor can't accidentally hide a
  broken-home-page warning. Implementation is now hook-driven and
  testable in isolation.

Migrations

• admin_notice_dismissals table (one alembic revision).