test: add core test suite for crypto, auth, and store packages

- 8 crypto tests: key derivation, encrypt/decrypt round-trip, wrong key, nonce uniqueness
- 6 auth tests: password hash/verify, JWT generate/validate, token revocation
- 14 store tests: project CRUD, user CRUD, stage/deploy lifecycle, pagination, cascade deletes
- Fix stages CREATE TABLE schema to include notification_url column
- Total: 28 tests, all passing

internal/store/store.go

@@ -167,7 +167,8 @@ CREATE TABLE IF NOT EXISTS stages (
 	confirm       INTEGER NOT NULL DEFAULT 0,
 	enable_proxy  INTEGER NOT NULL DEFAULT 1,
 	promote_from  TEXT NOT NULL DEFAULT '',
-	subdomain     TEXT NOT NULL DEFAULT '',
+	subdomain         TEXT NOT NULL DEFAULT '',
+	notification_url  TEXT NOT NULL DEFAULT '',
 	created_at    TEXT NOT NULL DEFAULT (datetime('now')),
 	updated_at    TEXT NOT NULL DEFAULT (datetime('now')),
 	UNIQUE(project_id, name)