Add integration tests for ProfilesClient and switchLlm

[VascoSch92]

Follow-up to #148. That PR adds ProfilesClient and RemoteConversation.switchLlm, but ships unit tests only (mocked global.fetch). Mocked tests verify wire shape but don't catch server-side drift.

Tasks

Can be done today (endpoints exist on main):

• Profiles CRUD round-trip integration test: save → get → list → activate → rename → delete against a running agent-server.
• Add a switchLlm assertion in src/__tests__/integration/deterministic-api.integration.test.ts next to the existing switchProfile 404 check.

Blocked on OpenHands/software-agent-sdk#3161 merging and a released agent-server image:

• End-to-end coverage of X-Expose-Secrets: encrypted | plaintext (cipher round-trip).

Note: integration tests run via npm run test:integration against a live agent-server; they aren't in the default npm test suite.