Merge origin/main into feature/assign-archetypes-to-tasks-ui

Resolved conflicts:
- .gitignore: kept both bd.sock.startlock and .beadboard/ entries
- package.json: kept feature branch test script (explicit enumeration)
- API routes: kept dynamic export + isValidProjectRoot from main
- globals.css: kept HEAD slideInFromRight animation
- use-beads-subscription.ts: kept HEAD onopen handler
- realtime.ts: kept main console.log in emit()
- snapshot-differ.ts: kept main type-aware dependency diff

Blue colors preserved from feature branch.

.gitignore

@@ -13,5 +13,9 @@ worktrees/
 
 # local screenshot artifacts
 artifacts/
+
+# beads socket lock
 .beads/bd.sock.startlock
-.beads/bd.sock.startlock
+
+# beadboard runtime artifacts
+.beadboard/