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>

packages/shared-ui/src/navigation/PillNavigation.svelte

@@ -943,6 +943,19 @@
 					</svg>
 					<span class="pill-label">Logout</span>
 				</button>
+			{:else if loginHref && !userEmail}
+				<!-- Guest mode: prominent login button -->
+				<a href={loginHref} class="pill glass-pill login-pill" title="Anmelden">
+					<svg class="pill-icon" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path
+							stroke-linecap="round"
+							stroke-linejoin="round"
+							stroke-width="2"
+							d={getIconPath('user')}
+						/>
+					</svg>
+					<span class="pill-label">Anmelden</span>
+				</a>
 			{/if}
 
 			<!-- Collapse Button -->
@@ -1111,6 +1124,20 @@
 		border-color: rgba(220, 38, 38, 0.3);
 	}
 
+	/* Guest login pill — prominent with primary color */
+	.login-pill {
+		background: var(--pill-primary-color, var(--color-primary-500, #3b82f6));
+		color: #fff;
+		border-color: transparent;
+		font-weight: 600;
+		text-decoration: none;
+	}
+
+	.login-pill:hover {
+		filter: brightness(1.1);
+		transform: scale(1.03);
+	}
+
 	.pill-icon {
 		width: 1rem;
 		height: 1rem;