perf: SW cache for indexed reads + denormalised image dimensions

[karlitschek]

Two related performance changes that show up most when navigating between Photos / Videos / Favorites tabs and on big libraries.

Service-worker runtime cache (vite.config.ts)

• The SW was already registered with one CacheFirst rule for the preview endpoint. Added strategies for the indexed-read paths the perf-index branch introduced: /api/v1/index/timeline → StaleWhileRevalidate (200 entries, 6h TTL). Returns the previous response instantly for tab transitions while the SW kicks off a fresh fetch in the background — feels "instant" on repeat visits. /api/v1/index/search → NetworkFirst with 4s timeout fall-back (50 entries, 30s TTL). Search wants freshness; the cache is only there to keep the previous results visible while the new query lands. /api/v1/index/status → NetworkFirst with 3s timeout fall-back (4 entries, 60s TTL). Migration banner needs near-real-time updates while the backfill runs. /api/v1/transcode/{id}/seg-N.ts → CacheFirst (2000 entries, 30d TTL). Segments are content-addressed so safe to cache aggressively.
• Existing preview cache rule generalised to also match publicPreview (was missing on shared-album views).

Denormalised image dimensions on oc_photos_index

• New migration adds width / height (nullable INT UNSIGNED).
• PhotoIndexService now reads photos-size via IFilesMetadataManager at index time and writes both columns alongside the existing taken_at. NULL until metadata is ready — the metadata pipeline is async, so a freshly-written file may hit the listener before its size is computed; a subsequent NodeWritten / backfill pass fills the columns.
• extractTakenAt now delegates to a shared extractIndexFields so the metadata read path is one method, not two slightly- different ones drifting over time.
• Mapper SELECTs (getEnrichedTimelineForUser, searchUserTimeline) return width/height; the GROUP BY adds them to the keyed columns.
• IndexController.composeItem reads photos-size from the row first, falls back to the metadata blob for old rows that haven't been re-indexed since the migration. Frontend keeps reading attributes['metadata-photos-size'].width/height — same shape in the response, just sourced from the index table.

Bumped app version to 7.0.0-dev.3 so occ upgrade re-runs the migration loader.

[karlitschek]

@jancborchardt @AndyScherzinger @artemanufrij @skjnldsv @artonge

[codecov]

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