refactor(frontend): major rebuild — feature-sliced architecture + bug fixes + glass-morphism UI

Architecture:
- Feature-sliced directory: entities/, shared/, features/, widgets/
- Consolidated API client (shared/api/client.ts) — all endpoints in one file
- Single WebSocket manager (shared/ws/socket.ts) with typed event bus
- Extracted hooks: useAudioPlayback, useAudioTransmit, useLocalStorage, useUIState
- UI primitives moved to shared/ui/ with barrel export
- Added Skeleton, Toast, MobileTabBar components

Bug fixes (8/8):
1. useMemo→useEffect in RecordingsSubPanel (async side-effect anti-pattern)
2. ArrayBuffer.slice() before WebSocket send (shared buffer bug)
3. Proper useEffect dependency arrays throughout
4. Stable React keys (no index fallbacks)
5. onReanalyze properly awaited (Promise<void> return)
6. monitorGuild memoized with useMemo
7. localStorage validation with shape checking
8. Deleted duplicate socket logic (ws/client.ts removed)

UI polish:
- Glass-morphism design tokens (backdrop-blur, translucent cards)
- Gradient mesh background with subtle radial overlays
- Expandable sidebar + mobile bottom tab bar
- Skeleton loading placeholders
- Audio visualizer with CSS pulse animation

Deleted: src/api/, src/components/, src/hooks/, src/types/, src/ws/, src/lib/
Added: 40 new files across feature-sliced structure

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/messages/hooks/useMessages.ts

@@ -0,0 +1,55 @@
+import { useCallback, useState } from "react";
+import { listMessages, reanalyzeMessage } from "../../../shared/api/client";
+import type { MessageRecord } from "../../../shared/api/client";
+
+export function mergeMessages(current: MessageRecord[], incoming: MessageRecord[]): MessageRecord[] {
+  const byId = new Map(current.map((message) => [message.id, message]));
+  for (const message of incoming) {
+    byId.set(message.id, { ...byId.get(message.id), ...message });
+  }
+  return Array.from(byId.values())
+    .sort((a, b) => b.created_at - a.created_at || b.id.localeCompare(a.id))
+    .slice(0, 200);
+}
+
+export function useMessages() {
+  const [messages, setMessages] = useState<MessageRecord[]>([]);
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const fetchMessages = useCallback(async (channelId?: string) => {
+    if (!channelId) {
+      setMessages([]);
+      return [];
+    }
+    setLoading(true);
+    setError(null);
+    try {
+      const params = new URLSearchParams({ limit: "80" });
+      params.set("channel", channelId);
+      const result = await listMessages(params);
+      setMessages(result.data);
+      return result.data;
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err);
+      setError(message);
+      throw err;
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  // BUG 5 FIX: reanalyze returns Promise<void> so callers can await it
+  const reanalyze = useCallback(async (id: string): Promise<void> => {
+    setMessages((prev) =>
+      prev.map((message) =>
+        message.id === id
+          ? { ...message, ai_status: "pending" as const, ai_error: null, ai_analysis: null }
+          : message,
+      ),
+    );
+    await reanalyzeMessage(id);
+  }, []);
+
+  return { messages, setMessages, loading, error, fetchMessages, reanalyze };
+}