feat: task 1.8 logout flow + cross-tab sync + strict tsconfig

- src/auth/logout.ts: performLogout({ queryClient, navigate? })
  orchestration. Calls store.logout(), clears query cache, navigates
  to /login. Server-call failures swallowed; local state still flips
  to anonymous.
- src/auth/cross-tab-sync.ts: startCrossTabSync(). Subscribes to the
  auth store and bumps trm-auth-version in localStorage on status
  transitions; listens for storage events and re-runs initialize()
  when another tab bumps. Idempotent via module-level guard. No-ops
  if localStorage is unavailable.
- src/ui/components/logout-button.tsx: <LogoutButton> wraps shadcn
  Button. Pass-through props but locks onClick / disabled / children.
  Local isLoggingOut for "Signing out..." indicator + double-click
  guard.
- src/auth/bootstrap.tsx: <AuthBootstrap> now calls startCrossTabSync()
  alongside the existing init steps. Single mount point.
- src/auth/index.ts: re-export performLogout + startCrossTabSync.
- src/routes/_authed/index.tsx: replaced the inline sign-out button
  with <LogoutButton />. The existing useEffect on 'anonymous' status
  handles navigation when cross-tab sync fires.

Bonus: tsconfig.app.json now has "strict": true. TanStack Router emits
a conditional-type error ("strictNullChecks must be enabled") in
editors when strict is off; tsc -b was lenient. Caught in 1.7's
review. Typecheck remained green after enabling.

tsconfig.app.json

@@ -21,6 +21,7 @@
     },
 
     /* Linting */
+    "strict": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,
     "erasableSyntaxOnly": true,