fix(db): scope, evict, and cap the offline blob cache (H3) (#1178)

Blob cache previously leaked forever: clearTripData omitted it, entries had
no trip discriminator, and there was no size/count bound, so file blobs
survived trip eviction and could starve the map-tile cache for quota.

- BlobCacheEntry gains tripId + bytes; Dexie v3 adds a tripId index with a
  backfill upgrade (legacy rows -> tripId -1, bytes from blob.size)
- clearTripData purges the trip's blobs in-transaction
- enforceBlobBudget() evicts oldest-by-cachedAt past 200 entries / 100 MB
- tripSyncManager threads tripId/bytes into puts and enforces the budget

client/src/sync/tripSyncManager.ts

@@ -27,6 +27,7 @@ import {
   upsertCategories,
   upsertSyncMeta,
   clearTripData,
+  enforceBlobBudget,
 } from '../db/offlineDb'
 import { prefetchTilesForTrip } from './tilePrefetcher'
 import { isAuthed } from './authGate'
@@ -109,13 +110,16 @@ async function cacheFilesForTrip(files: TripFile[]): Promise<void> {
       const resp = await fetch(file.url!, { credentials: 'include' })
       if (!resp.ok) continue
       const blob = await resp.blob()
-      await offlineDb.blobCache.put({ url: file.url!, blob, mime: file.mime_type, cachedAt: Date.now() })
+      await offlineDb.blobCache.put({ url: file.url!, tripId: file.trip_id, blob, bytes: blob.size, mime: file.mime_type, cachedAt: Date.now() })
       cached++
     } catch {
       // Network failure — skip this file, will retry next sync
     }
   }
 
+  // Keep the blob cache within its size/count budget after adding new files.
+  if (cached > 0) await enforceBlobBudget().catch(() => {})
+
   // Update filesCachedCount in syncMeta
   const tripId = files[0]?.trip_id
   if (tripId) {