watchlist routes: convert 8 routes to TanStack route loaders + error component convention

[electather]

Part of epic #491. Owner direction repeated on 8 route files:

use route loader for the content of the page.
use tanstack router convention for error boundary.

Routes (8)

• apps/client/src/routes/_authenticated/_app/watchlist.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.index.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.ready.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.in-progress.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.awaiting.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.upcoming.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.unavailable.tsx
• apps/client/src/routes/_authenticated/_app/watchlist.moods.$moodId.tsx

Goal

• Move data fetching out of component into route loader (or loaderDeps + loader).
• Use TanStack errorComponent route option instead of in-component <ErrorBoundary> wrapper.
• Page components consume loader data via Route.useLoaderData() / suspense queries.

Bonus item

watchlist.moods.$moodId.tsx:16 — review comment "is this needed?". Verify the line in question and remove if dead.

Acceptance criteria

• All 8 routes use route loaders.
• All 8 routes use errorComponent route option (no <ErrorBoundary> wrappers in components).
• V.WL1–V.WL11 invariants still pinned.
• Typecheck passes.
• Verify in browser: cold load, navigation between buckets, mood detail all render correctly; error states route to errorComponent.