feat(apps): migrate Presi, Picture, Inventar, NutriPhi, Planta, Storage to local-first

Add IndexedDB data layer (Dexie.js via @manacore/local-store) to 6 more apps,
bringing the total to 12/22 apps with local-first architecture.

For each app:
- Create local-store.ts with typed collections and sync config
- Create guest-seed.ts with onboarding data for guest mode
- Update layout with AuthGate allowGuest={true} + handleAuthReady()
- Add GuestWelcomeModal for first-visit experience
- Add @manacore/local-store dependency

App-specific changes:
- Presi: Rewrite decks store from API to IndexedDB, conditional share button
- Picture: Rewrite gallery + boards pages to read from IndexedDB
- Inventar: Replace manual auth $effect with AuthGate, keep localStorage stores
- NutriPhi: Add onReady handler to existing AuthGate
- Planta: Add allowGuest + sync init to existing AuthGate
- Storage: Add local store init to existing handleAuthReady

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/plans/local-first-architecture-migration.md

@@ -313,7 +313,7 @@ apps/todo/apps/backend/     # Oder: services/todo/ (umstrukturieren?)
 
 ---
 
-## Phase 3: Rollout auf alle Apps (4-6 Wochen) — 6/8 DONE 2026-03-27
+## Phase 3: Rollout auf alle Apps (4-6 Wochen) — 8/8 DONE 2026-03-27
 
 Reihenfolge nach Komplexität: