refactor: atomic, DRY, and logging improvements across codebase

- Split llmModerationClient.ts (2170 lines) into 5 focused sub-modules
- Split aiAnalyzer.ts (1282 lines) into 4 modular pipelines
- Split messages.db.ts (826 lines) into 5 domain-specific modules
- Moved shared schema to @bete/shared, eliminated backend duplication
- Added createChildLogger to all voice-recording and AI moderation modules
- Extracted tryCommandThenFallback, normalizeMediaState, DEFAULT_VOICE_STATUS
- Created shared pagination.ts utility, eliminated 5+ cursor-pagination duplications
- Created shared messageMapper.ts for row mapping
- Standardized backend error handling with asyncHandler
- Added frontend createLogger utility and useAsyncAction hook
- Added structured logging to frontend hooks, socket, and API client

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

packages/shared/src/utils/index.ts

@@ -4,6 +4,8 @@ export function delay(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
 
+export * from "./pagination.js";
+
 // ---------------------------------------------------------------------------
 // Retry with exponential backoff
 // ---------------------------------------------------------------------------

packages/shared/src/utils/pagination.ts

@@ -0,0 +1,65 @@
+// Shared cursor-based pagination utilities
+
+export interface CursorData {
+  created_at: number;
+  id: string;
+}
+
+/**
+ * Encode a cursor to a base64 string.
+ */
+export function encodeCursor(data: CursorData): string {
+  return Buffer.from(JSON.stringify(data)).toString("base64");
+}
+
+/**
+ * Decode a cursor from a base64 string. Returns null on invalid input.
+ */
+export function decodeCursor(cursor?: string): CursorData | null {
+  if (!cursor) return null;
+  try {
+    const data = JSON.parse(Buffer.from(cursor, "base64").toString("utf-8"));
+    if (typeof data.created_at === "number" && typeof data.id === "string") {
+      return data;
+    }
+    return null;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Build a `PageResult` from a slice of rows (limit + 1) using cursor-based pagination.
+ */
+export function pageResult<T extends { created_at: number; id: string }>(
+  rows: unknown[],
+  limit: number,
+): { data: T[]; nextCursor: string | null } {
+  const hasMore = rows.length > limit;
+  const data = rows.slice(0, limit) as T[];
+  const lastItem = data[data.length - 1];
+  const nextCursor =
+    hasMore && lastItem
+      ? encodeCursor({ created_at: lastItem.created_at, id: lastItem.id })
+      : null;
+
+  return { data, nextCursor };
+}
+
+/**
+ * Build a Drizzle cursor condition expression.
+ * Used in WHERE clauses: `(created_at < cursor.created_at OR (created_at = cursor.created_at AND id < cursor.id))`
+ *
+ * Returns the SQL expression or undefined when cursor is absent.
+ */
+import { type SQL, sql } from "drizzle-orm";
+
+export function buildCursorCondition(
+  created_at_col: SQL | unknown,
+  id_col: SQL | unknown,
+  cursor?: string,
+): SQL | undefined {
+  const data = decodeCursor(cursor);
+  if (!data) return undefined;
+  return sql`(${created_at_col} < ${data.created_at} or (${created_at_col} = ${data.created_at} and ${id_col} < ${data.id}))`;
+}