gleam: write integration tests (same 8 cases as Go/TS)

[HeyItWorked]

Task

Create gleam-bookshelf/test/handlers_test.gleam and gleam-bookshelf/test/test_helpers.gleam.

Test cases (same 8 as Go and TS)

1. create book — POST /books → 201, check title/author/status/id
2. get books — GET /books → 200, non-empty list
3. get book — GET /books/:id → 200, check fields present
4. get book not found — GET /books/99999 → 404
5. update book — PUT /books/:id → 200, check status changed
6. delete book — DELETE /books/:id → 204
7. create book no title — POST /books → 400
8. create book invalid status — POST /books → 400

Test helpers needed

• setup() -> Context — connect to Postgres, return context
• send_request(method, path, body, ctx) -> Response — send request through router
• send_and_expect(method, path, body, expected_status, ctx) -> Response

Key differences from Go/TS

• Uses gleeunit or startest for test framework
• No TestMain or beforeAll — setup function called explicitly
• Assertions: should.equal(value, expected) pattern
• Like TS version, capture bookId from create for use in later tests

Acceptance criteria

• All 8 test cases pass against real Postgres (no mocks)
• gleam test succeeds with DATABASE_URL set