feat: add docs app with Fumadocs

- Add `docs/` — Next.js 15 app powered by Fumadocs with a landing page, docs layout, search, OG image generation, and LLM text routes
- Cover getting started, configuration, integrations (Plex, Emby, Jellyfin, Radarr, Sonarr), mobile app setup, and telemetry in MDX
- Exclude `docs/` from root Biome config since it has its own `biome.json`

docs/biome.json

@@ -0,0 +1,40 @@
+{
+  "$schema": "./node_modules/@biomejs/biome/configuration_schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "files": {
+    "ignoreUnknown": true,
+    "includes": ["**", "!node_modules", "!.next", "!dist", "!build", "!.source"]
+  },
+  "css": {
+    "parser": {
+      "cssModules": true,
+      "tailwindDirectives": true
+    }
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true
+    },
+    "domains": {
+      "next": "recommended",
+      "react": "recommended"
+    }
+  },
+  "assist": {
+    "actions": {
+      "source": {
+        "organizeImports": "on"
+      }
+    }
+  }
+}