Advertise form elicitation in client

[caseychow-oai]

Summary

Align client elicitation behavior with what is actually handled:

• advertise form elicitation support explicitly
• decline URL-mode elicitation requests

What Changed

• client/src/lib/hooks/useConnection.ts
  • changes client capabilities from elicitation: {} to elicitation: { form: {} }
  • adds URL-mode guard in the elicitation/create handler returning { action: "decline" }
• client/src/lib/hooks/__tests__/useConnection.test.tsx
  • updates capability expectation to assert elicitation.form
  • adds test coverage that URL-mode elicitation is declined and not forwarded to onElicitationRequest

Why

The client should only declare/support elicitation modes it can handle. This keeps capability advertisement and runtime behavior consistent.

Testing

• cd client && npm test -- --runTestsByPath src/lib/hooks/__tests__/useConnection.test.tsx --watch=false
• Result: pass (42 tests)

Breaking Changes

None.

AI Disclosure

This PR was prepared with assistance from an AI coding agent.