feat(auth): user-management audit log (table + record sites + /api/audit endpoint)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/data/audit.ts

@@ -0,0 +1,56 @@
+import type Database from "better-sqlite3";
+
+export type AuditAction =
+  | "admin.first_created"
+  | "user.created"
+  | "user.deleted"
+  | "user.password_reset"
+  | "user.password_changed";
+
+export interface AuditEntry {
+  id: number;
+  timestamp: number;
+  actorId: string | null;
+  actorUsername: string | null;
+  targetUserId: string | null;
+  targetUsername: string | null;
+  action: AuditAction;
+}
+
+export interface AuditRecordInput {
+  actorId: string | null;
+  actorUsername: string | null;
+  targetUserId: string | null;
+  targetUsername: string | null;
+  action: AuditAction;
+}
+
+export interface AuditStore {
+  record(input: AuditRecordInput): void;
+  list(limit: number, offset: number): AuditEntry[];
+}
+
+export function createAuditStore(db: Database.Database): AuditStore {
+  const insertStmt = db.prepare(
+    "INSERT INTO user_audit (timestamp, actorId, actorUsername, targetUserId, targetUsername, action) VALUES (?, ?, ?, ?, ?, ?)"
+  );
+  const listStmt = db.prepare(
+    "SELECT id, timestamp, actorId, actorUsername, targetUserId, targetUsername, action FROM user_audit ORDER BY timestamp DESC, id DESC LIMIT ? OFFSET ?"
+  );
+
+  return {
+    record(input) {
+      insertStmt.run(
+        Date.now(),
+        input.actorId,
+        input.actorUsername,
+        input.targetUserId,
+        input.targetUsername,
+        input.action
+      );
+    },
+    list(limit, offset) {
+      return listStmt.all(limit, offset) as AuditEntry[];
+    },
+  };
+}