feat(frontend): implement file viewer page with metadata editing and tag picker
- files/[id]/+page.svelte: full-screen preview (100dvh), sticky top bar,
prev/next nav via anchor API, notes/datetime/is_public editing, TagPicker,
EXIF display, keyboard navigation (←/→/Esc)
- TagPicker.svelte: assigned tags with remove, searchable available tags to add
- Fix infinite request loop: previewSrc read inside $effect tracked as dependency;
wrapped in untrack() to prevent re-triggering on blob URL assignment
- vite-mock-plugin: add GET/PATCH /files/{id}, preview endpoint, tags CRUD,
anchor-based pagination, in-memory mutable state for file overrides and tags
- files/+page.svelte: migrate from deprecated $app/stores to $app/state
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Masahiko AMANO
a5b610d472