feat: migrate Leptos frontend to Next.js 16 (React 19)

Complete migration from services/frontend.old/ (Leptos 0.7 WASM + Rust)
to services/frontend/ (Next.js 16 static export + TypeScript + Tailwind v4).

Summary:
- Port all shared types (message, guild, voice, media, dashboard, recording, ui)
- Build fetch-based API client covering all 30+ backend endpoints
- WebSocket client with auto-reconnect (exponential backoff, 20 attempts)
- React context provider for WS with typed event subscription (22 event types)
- Login page with localStorage auth + auto-redirect
- Dashboard layout with sidebar, header (WS status + theme toggle)
- Messages: feed, search, images tab, review tab, channel filter, detail modal
- Live: voice connection, music player, recordings, mic transmit, active speakers
- Dashboard: stats, user list, channel list, detail views
- Mascot chatbot with history + clear
- uiStateApi persistence for selected tab
- Add static export config, update deploy scripts and CI

services/frontend/biome.json

@@ -0,0 +1,53 @@
+{
+  "$schema": "https://biomejs.dev/schemas/2.2.0/schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "files": {
+    "ignoreUnknown": true,
+    "includes": ["**", "!node_modules", "!.next", "!dist", "!build"]
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true,
+      "suspicious": {
+        "noUnknownAtRules": "off",
+        "useIterableCallbackReturn": "off",
+        "noArrayIndexKey": "warn"
+      },
+      "a11y": {
+        "useButtonType": "off",
+        "noAutofocus": "off"
+      },
+      "performance": {
+        "noImgElement": "warn"
+      },
+      "security": {
+        "noDangerouslySetInnerHtml": "warn"
+      },
+      "correctness": {
+        "noInvalidUseBeforeDeclaration": "off",
+        "noUnusedFunctionParameters": "warn"
+      }
+    },
+    "domains": {
+      "next": "recommended",
+      "react": "recommended"
+    }
+  },
+  "assist": {
+    "actions": {
+      "source": {
+        "organizeImports": "on"
+      }
+    }
+  }
+}