[TAG-02] Add web and desktop tag actions and filters #12

ID: TAG-02 (TAG-001). Priority: P1. Blocked by: #11. Backlog: #1.

Scope and acceptance criteria

• Add web/desktop thread actions to assign/remove manual tags, compact chips
  in flat and repository-grouped lists, and settings management for
  rename/archive/restore. Existing contexts invoke the same commands.
• Show at most two chips plus an accessible count; label/source/freshness is
  available without relying on color. Manual and derived same-label tags stay
  distinguishable. Stale derived tags are visibly stale.
• Filters use exact scoped tag IDs and OR selected tags by default. Keep
  definitions from different environments distinct; same-label automatic
  aggregation is out of scope. Opening a result uses normal scoped routing.
• Include active/archived and derived stale visibility controls where relevant.
  Local hiding never deletes derived assignments; clear filters and unhide
  paths are available.
• Handle concurrent edit conflicts visibly, refetch authorized current data and
  never claim a failed mutation succeeded. Disconnected clients may inspect
  cached tags but cannot derive or confirm new assignments.
• Large lists use compact indexed summaries and bounded queries, not full
  thread data. Test actions, filters, archive/restore, remote deltas, disabled
  mutations offline, source distinction and accessible keyboard navigation.

Reuse, coverage and non-goals

Reuse upstream thread menus, settings, search/filter and sidebar grouping.
Desktop wraps web; local and hosted web plus all remote environments/providers.
Mobile UI is TAG-03. No derived-tag reconciliation engine, turn tags, global
definitions, automatic same-label merge or new routing model.