feat(local-first): add local-first architecture with Dexie.js, Go sync server, and Todo pilot

Implement the foundational local-first data layer for ManaCore apps:

- New @manacore/local-store package (Dexie.js IndexedDB, sync engine, Svelte 5 reactive queries)
- New mana-sync Go service (sync protocol, WebSocket push, field-level LWW conflict resolution)
- Todo app migrated as pilot: stores read/write IndexedDB, guest mode with onboarding seed data
- PillNavigation: prominent login pill for unauthenticated users
- SyncIndicator component showing local/syncing/offline status
- GuestWelcomeModal on first visit for Todo app
- Removed demo-mode auth_required checks from Todo components (all writes are now local)
- CSP fix for local development (localhost:3001, localhost:3050)

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

services/mana-sync/package.json

@@ -0,0 +1,11 @@
+{
+	"name": "@mana-sync/service",
+	"version": "0.1.0",
+	"private": true,
+	"description": "Central sync server for ManaCore local-first apps (Go)",
+	"scripts": {
+		"dev": "go run ./cmd/server",
+		"build": "go build -o dist/mana-sync ./cmd/server",
+		"test": "go test ./..."
+	}
+}