📝 docs: add Astro Starlight public documentation site

Add comprehensive documentation site using Astro Starlight with:
- Getting Started guides (introduction, quick-start, project structure)
- Development docs (local dev, env vars, docker, migrations, testing)
- Architecture docs (overview, auth, backend, web, mobile, storage, search)
- Guidelines (code style, error handling, database, design/UX)
- Deployment docs (overview, Cloudflare Pages, Mac Mini, self-hosting)
- Project pages (overview, chat)
- API reference structure

Features:
- Dark mode support
- Full-text search (Pagefind)
- Tailwind CSS styling
- Cloudflare Pages deployment ready
- Edit on GitHub links

apps/docs/src/styles/custom.css

@@ -0,0 +1,66 @@
+/* Manacore Docs - Custom Starlight Styles */
+
+/* Override Starlight CSS variables */
+:root {
+	--sl-color-accent-low: #0c4a6e;
+	--sl-color-accent: #0ea5e9;
+	--sl-color-accent-high: #bae6fd;
+	--sl-color-white: #ffffff;
+	--sl-color-gray-1: #f1f5f9;
+	--sl-color-gray-2: #e2e8f0;
+	--sl-color-gray-3: #cbd5e1;
+	--sl-color-gray-4: #94a3b8;
+	--sl-color-gray-5: #64748b;
+	--sl-color-gray-6: #475569;
+	--sl-color-black: #0f172a;
+}
+
+:root[data-theme='dark'] {
+	--sl-color-accent-low: #082f49;
+	--sl-color-accent: #0ea5e9;
+	--sl-color-accent-high: #7dd3fc;
+	--sl-color-white: #0f172a;
+	--sl-color-gray-1: #1e293b;
+	--sl-color-gray-2: #334155;
+	--sl-color-gray-3: #475569;
+	--sl-color-gray-4: #64748b;
+	--sl-color-gray-5: #94a3b8;
+	--sl-color-gray-6: #cbd5e1;
+	--sl-color-black: #f8fafc;
+}
+
+/* Custom font settings */
+html {
+	font-family: 'Inter', system-ui, sans-serif;
+}
+
+code,
+pre {
+	font-family: 'JetBrains Mono', 'Menlo', monospace;
+}
+
+/* Better code block styling */
+.expressive-code pre {
+	border-radius: 0.5rem;
+}
+
+/* Sidebar improvements */
+.sidebar-content {
+	scrollbar-width: thin;
+}
+
+/* Custom badge styles for project status */
+.badge-stable {
+	background-color: #10b981;
+	color: white;
+}
+
+.badge-beta {
+	background-color: #f59e0b;
+	color: white;
+}
+
+.badge-alpha {
+	background-color: #ef4444;
+	color: white;
+}