feat(live): per-user favorite cameras with a Live view filter

[matteius]

Summary

Replacement for the favorites half of #624 (thanks @zirocool93 for the idea and the groundwork). Each signed-in user gets a personal set of favorite cameras: a star on every Live tile adds or removes a camera, and a Favorites toggle in the Live toolbar filters the grid. The filter is persisted in the URL (?favorites=1) like the collection and tag filters.

Unlike #624 this lives inside the existing LiveView rather than a separate mobile surface, has no forced UI-mode selector, and every string goes through i18n.

Design notes

• Dedicated table, not a collection. Camera collections have a globally unique name and default to shared, and saved layouts are grids, so neither models a private per-user camera set without schema contortions. Migration 0088 adds camera_favorites(user_id, camera_uuid, created_at) with cascading deletes from users and streams.
• Auth-disabled installs. A NULL user_id holds the single installation-wide set, the same convention live_saved_layouts uses for its owner, so favorites work without logins.
• Scope. GET only returns cameras inside the caller's current live-view scope (same AUTHZ_LIVE_VIEW filter as layouts). PUT answers 404 for unknown and out-of-scope cameras alike. Demo and scoped-token identities are read-only.
• Not audited. Favorites are a personal preference, not camera configuration.

API

GET    /api/camera-favorites                 -> {favorites:[{camera_uuid, created_at}], can_modify}
PUT    /api/camera-favorites/{camera_uuid}   -> the record (idempotent)
DELETE /api/camera-favorites/{camera_uuid}   -> {success, removed} (idempotent)

Documented in docs/API.md under Camera Favorites.

Frontend

• web/js/components/preact/live/cameraFavorites.js: pure helpers (set derivation, filtering, cache update, request shape) plus useCameraFavorites() over the query cache with optimistic cache update and invalidation.
• LiveView.jsx: toolbar toggle (shown when the user can modify favorites or already has some), tile star overlay (hidden in reorder mode and when controls are hidden), favorites-aware empty state. A stale ?favorites=1 does not blank the grid if favorites are unavailable.
• Star styling in live.css, larger hit target on coarse pointers.

Testing

• test_db_camera_favorites (6): idempotent add keeps created_at, per-user scoping, installation scope without a user, invalid and unknown cameras, user-deletion cascade, soft vs permanent stream deletion.
• test_api_handlers_camera_favorites (3): put/list/delete round trip, 400/404 paths, demo identity read-only with 403 on writes.
• web/tests/cameraFavorites.spec.js (4): set derivation and filtering, cache update ordering, request method and UUID encoding, failure propagation.
• All targets build clean; npx vite build clean; Jest 311/311; full ctest 144/145 with the one failure being the known local FFmpeg header mismatch in test_mp4_segment_boundaries.
• Not yet exercised in a browser against a running server; the hook and handlers are covered by unit tests.

Not included

• Favorites on the recordings page or in the operator navigator. The API is page-agnostic, so those are follow-ups.
• The mobile-specific live surface and UI-mode selector from Codex/mobile live favorites #624.

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