Add sessions, users tables to schema

api/db/migrations/20260829174406_create_auth_tables.sql

@@ -0,0 +1,21 @@
+-- migrate:up
+CREATE TABLE  users (
+    id SERIAL PRIMARY KEY,
+    username TEXT UNIQUE NOT NULL,
+    password_hash TEXT NOT NULL,
+    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL
+);
+
+CREATE TABLE sessions (
+    id VARCHAR(64) PRIMARY KEY,
+    user_id INT REFERENCES users(id) ON DELETE CASCADE NOT NULL,
+    expires_at TIMESTAMPTZ NOT NULL,
+    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL
+);
+
+CREATE INDEX idx_sessions_expires_at ON sessions(expires_at);
+
+-- migrate:down
+DROP TABLE sessions;
+DROP TABLE users;
+