Phase 2: auth, session management, layout, PWA manifest

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

internal/db/schema.sql

@@ -47,6 +47,13 @@ CREATE TABLE IF NOT EXISTS user_question_stats (
   PRIMARY KEY (user_id, question_id)
 );
 
+CREATE TABLE IF NOT EXISTS sessions (
+  token TEXT PRIMARY KEY,
+  data BLOB NOT NULL,
+  expiry INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS idx_sessions_expiry ON sessions(expiry);
+
 CREATE INDEX IF NOT EXISTS idx_test_answers_test ON test_answers(test_id);
 CREATE INDEX IF NOT EXISTS idx_answers_question ON answers(question_id);
 CREATE INDEX IF NOT EXISTS idx_stats_user ON user_question_stats(user_id);