Phase 7: Search, filters, templates, and archive UI

Add full-text card search (PostgreSQL tsvector + GIN index) with navbar
SearchBar, client-side board filters (label/assignee/due date), board
templates (3 system templates + save-as-template API), and archive
toggle for both board listing and board view.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/setup-search.sql

@@ -0,0 +1,9 @@
+-- Full-text search on cards
+-- Generated tsvector column + GIN index for fast searching
+
+ALTER TABLE cards ADD COLUMN IF NOT EXISTS search_vector tsvector
+  GENERATED ALWAYS AS (
+    to_tsvector('english', coalesce(title, '') || ' ' || coalesce(description, ''))
+  ) STORED;
+
+CREATE INDEX IF NOT EXISTS cards_search_idx ON cards USING gin(search_vector);