feat(javascript): Add Sequelize ORM sample for Aurora DSQL

[lasitab-code]

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT-0 license.

Summary

Adds a Node.js sample demonstrating Sequelize ORM with Aurora DSQL, including:

• CRUD operations for a hotel reservation domain (guests, rooms, reservations, payments)
• IAM authentication (admin + non-admin user flows) via the Aurora DSQL node-postgres connector (dialectModule), with automatic token generation
  and Region discovery
• Foreign keys between the hotel entities
• OCC retry with exponential backoff and jitter
• Schema isolation for a least-privilege, non-admin application user
• Unit tests (Jest) and live integration tests

Testing

• End-to-end tested with admin and non-admin users against a live DSQL cluster (us-west-2)
• Unit tests pass: npm test (18 passed)
• Integration tests pass against a live cluster: npm run test:integration (5 passed); skip cleanly without credentials
• Security scan: 0 CVEs, 0 secrets, 0 code vulnerabilities

[praba2210]

Ran end-to-end on a real DSQL cluster - clean run, 4 FKs enforced, real OCC retry. Substance is solid; blockers are inline. Non-blocking:

Type	Where	Issue	Fix
should-fix	README.md:180	"write paths use the OCC retry helper" — only 1 of ~10 writes does. Wrap or soften.	Wrap the multi-step writes in withOccRetry, or reword to "…surface as retryable serialization errors — see retry.js, demonstrated on the loyalty-tier update".
should-fix	package.json	@aws-sdk/credential-providers + dsql-signer never imported — drop; regen lockfile (npm ci errors today).	npm uninstall @aws-sdk/credential-providers @aws-sdk/dsql-signer — drops both and syncs the lockfile in one step (verified: npm ci then passes, unit tests green; the connector still pulls both transitively).
should-fix	setup_app_user.sql:46-49	ADP rationale wrong: owners can't be denied own tables, and admin's ADP never covers app-created ones. Keep grant, fix comment.	Replace "Without this, the app hits permission denied on its own tables." with: this covers tables admin creates later in the schema; tables the app creates it already owns.
nit	db.js:78	createSchema() creates tables → createTables().	7 occurrences in 3 files: db.js:78,155; app.js:6,189; test/integration.test.js:32,39,45.
nit	README.md:183	Connector's occ-retry only wraps connect(); retry.js is the real mechanism — worth a line.	Add a clause to adaptation 5 — it explains why retry.js exists.
nit	test/test_example.test.js:39	Backoff timing unasserted (counts/give-up well covered).	Spy on setTimeout, force 3 OCC failures, assert each delay is in [50·2^i, 100·2^i) — covers exponent and jitter.
nit	headers	SPDX Apache-2.0 vs package.json MIT-0 — align.	Switch the 8 headers to MIT-0 (matches LICENSE, package.json:36, README.md:235), though other samples are mixed.

[praba2210]

No test executes this file — main() runs at import and nothing is exported, so both suites only test the helpers. Verified: injected a ~24% billing bug and a crash bug; all 23 tests stayed green both times.

Suggest the sibling pattern (node-postgres, batch_operations):

export { main };
if (import.meta.url === `file://${process.argv[1]}`) {
  main().catch((err) => { console.error(err); process.exit(1); });
}

then run main() from the integration test.

[praba2210]

searchPath makes Sequelize disable bind parameters — every model INSERT/UPDATE ships values inlined as literals (verified on the wire). Deleting this line restores $1, $2, … and queries stay schema-qualified via each model's schema: option. Ran the sample without it — identical behavior.

[praba2210]

Three documented steps fail as written:

1. Here — CLUSTER_REGION is "optional" per line 45 but this snippet requires it.
2. Line 213 — FK query filters table_schema = 'public'; the recommended hotel-schema path returns 0 rows vs "Expect four foreign keys".
3. setup_app_user.sql:38 — "run the app with CLUSTER_USER=admin" can't create the hotel tables; db.js:28-30 forces admin to public.