feat: implement moderation message capture system

- Add message store with database operations (insert, update, query)
- Implement attachment uploader with picser integration
- Add Discord event listeners for message create/update/delete
- Support attachment upload with retry logic and error handling
- Add comprehensive unit tests for message store and uploader

src/moderation/types.ts

@@ -0,0 +1,55 @@
+export interface MessageRecord {
+  id: string;
+  guild_id: string;
+  channel_id: string;
+  thread_id: string | null;
+  user_id: string;
+  username: string;
+  avatar_url: string | null;
+  content: string;
+  edited_content: string | null;
+  created_at: number;
+  edited_at: number | null;
+  deleted_at: number | null;
+  type: "text" | "edited" | "deleted";
+  metadata: string | null;
+}
+
+export interface AttachmentRecord {
+  id: string;
+  message_id: string;
+  guild_id: string;
+  channel_id: string;
+  user_id: string;
+  filename: string;
+  size: number;
+  type: string;
+  discord_url: string;
+  uploaded_url: string | null;
+  upload_status: "pending" | "uploaded" | "failed";
+  upload_error: string | null;
+  created_at: number;
+  uploaded_at: number | null;
+}
+
+export interface VoiceSegmentRecord {
+  id: string;
+  user_id: string;
+  session_id: string;
+  guild_id: string;
+  channel_id: string;
+  filename: string;
+  duration_ms: number;
+  created_at: number;
+}
+
+export interface DashboardMessage {
+  id: string;
+  channel_id: string;
+  user_id: string;
+  username: string;
+  avatar_url: string | null;
+  content: string;
+  created_at: number;
+  type: "text" | "image" | "voice";
+}