feat: implement user authentication system with admin dashboard

migrations/20260129200000_add_users_and_sessions.sql

@@ -0,0 +1,19 @@
+CREATE TABLE users (
+    discord_id BIGINT PRIMARY KEY,
+    discord_username TEXT NOT NULL,
+    discord_avatar_hash TEXT,
+    is_admin BOOLEAN NOT NULL DEFAULT false,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE TABLE user_sessions (
+    id TEXT PRIMARY KEY,
+    user_id BIGINT NOT NULL REFERENCES users(discord_id) ON DELETE CASCADE,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    expires_at TIMESTAMPTZ NOT NULL,
+    last_active_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX idx_user_sessions_user_id ON user_sessions(user_id);
+CREATE INDEX idx_user_sessions_expires_at ON user_sessions(expires_at);