Add PostgreSQL database layer with Kysely and migrations

- Add database.ts with connection pool, Kysely query builder, and migration runner
- Create migrations for users and sessions tables (0001, 0002)
- Implement PostgresAuthStore to replace InMemoryAuthStore
- Wire up database service in services/index.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

express/migrations/0001_users.sql

@@ -0,0 +1,21 @@
+-- 0001_users.sql
+-- Create users table for authentication
+
+CREATE TABLE users (
+    id UUID PRIMARY KEY,
+    email TEXT UNIQUE NOT NULL,
+    password_hash TEXT NOT NULL,
+    display_name TEXT,
+    status TEXT NOT NULL DEFAULT 'pending',
+    roles TEXT[] NOT NULL DEFAULT '{}',
+    permissions TEXT[] NOT NULL DEFAULT '{}',
+    email_verified BOOLEAN NOT NULL DEFAULT FALSE,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Index for email lookups (login)
+CREATE INDEX users_email_idx ON users (LOWER(email));
+
+-- Index for status filtering
+CREATE INDEX users_status_idx ON users (status);

express/migrations/0002_sessions.sql

@@ -0,0 +1,24 @@
+-- 0002_sessions.sql
+-- Create sessions table for auth tokens
+
+CREATE TABLE sessions (
+    token_id TEXT PRIMARY KEY,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    token_type TEXT NOT NULL,
+    auth_method TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    expires_at TIMESTAMPTZ NOT NULL,
+    last_used_at TIMESTAMPTZ,
+    user_agent TEXT,
+    ip_address TEXT,
+    is_used BOOLEAN DEFAULT FALSE
+);
+
+-- Index for user session lookups (logout all, etc.)
+CREATE INDEX sessions_user_id_idx ON sessions (user_id);
+
+-- Index for expiration cleanup
+CREATE INDEX sessions_expires_at_idx ON sessions (expires_at);
+
+-- Index for token type filtering
+CREATE INDEX sessions_token_type_idx ON sessions (token_type);