feat(db): add users and sessions tables for WebUI auth

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

src/data/database.ts

@@ -127,12 +127,33 @@ function initTables(db: Database.Database): void {
       serverPassword TEXT NOT NULL DEFAULT '',
       identity TEXT
     );
+
+    CREATE TABLE IF NOT EXISTS users (
+      id TEXT PRIMARY KEY,
+      username TEXT NOT NULL UNIQUE COLLATE NOCASE,
+      passwordHash TEXT NOT NULL,
+      createdAt INTEGER NOT NULL,
+      updatedAt INTEGER NOT NULL
+    );
+
+    CREATE TABLE IF NOT EXISTS sessions (
+      id TEXT PRIMARY KEY,
+      userId TEXT NOT NULL,
+      createdAt INTEGER NOT NULL,
+      expiresAt INTEGER NOT NULL,
+      lastSeenAt INTEGER NOT NULL,
+      FOREIGN KEY (userId) REFERENCES users(id) ON DELETE CASCADE
+    );
+
+    CREATE INDEX IF NOT EXISTS idx_sessions_userId ON sessions(userId);
+    CREATE INDEX IF NOT EXISTS idx_sessions_expiresAt ON sessions(expiresAt);
   `);
 }
 
 export function createDatabase(dbPath: string): BotDatabase {
   const db = new Database(dbPath);
   db.pragma("journal_mode = WAL");
+  db.pragma("foreign_keys = ON");
   initTables(db);
   migrateSchema(db);