feat: AI price estimation for shopping list with per-item real-time display

- Add get_shopping_price / get_all_shopping_prices API endpoints
- AI (Gemini) estimates retail price per natural unit (pack, piece, bunch)
  instead of always per-kg — avoids absurd totals like €1609
- _calcEstimatedTotal: proper g/ml→package conversion using defQty + regex
  on unit_label; only 'kg'/'l' labels trigger weight/volume math
- Cache key bumped to v2 to invalidate old per-kg cached entries
- Suggested quantity cap lowered from 20 to 10 conf/pz
- Unit mismatch guard: if totalUsed >> buyCount*5 for unit=conf, use
  purchase frequency instead of raw consumption rate
- JS _buildPricePayload: use smartShoppingItems for qty/unit (not Bring! spec)
- JS _cachedPrices: persist in sessionStorage (survives navigation);
  validated by _qty/_unit metadata so stale totals auto-invalidate
- Price display redesigned: right-side column per row (price-col-main +
  price-col-unit) instead of small inline badge
- fetchAllPrices: buttons disabled immediately before guard check;
  running total uses only current shoppingItems (not Object.values cache)
- Background refresh: always silent (removed 90s interaction condition)
- visibilitychange: sets _bgCall=true for shopping before refreshCurrentPage
- .gitignore: add runtime data files (bring_migrate_ts, shopping_price_cache,
  anomaly_dismissed, opened_shelf_cache, shopping_name_cache)
- Remove bring_catalog.json and bring_migrate_ts.json from tracking

.gitignore

@@ -11,6 +11,11 @@ data/cron.log
 data/smart_shopping_cache.json
 data/bring_token.json
 data/bring_catalog.json
+data/bring_migrate_ts.json
+data/shopping_price_cache.json
+data/anomaly_dismissed.json
+data/opened_shelf_cache.json
+data/shopping_name_cache.json
 data/client_debug.log
 data/rate_limits/