fix: make MCP elicitation support explicit and fail-closed

[rodaddy]

Found during the Herdr landed-PR review swarm for PR #41.

Problem

MCP elicitation support appears to auto-accept every server prompt with empty
content.

Evidence from the reviewed head:

• src/connection/capabilities.ts:18 returns accept behavior for elicitation
  requests.

For non-interactive CLI usage this should be explicit and fail-closed. A server
prompt should not be blanket-accepted without user policy, command-line opt-in,
or an application-provided response handler.

Acceptance criteria

• Non-interactive CLI behavior rejects, declines, or reports unsupported
  elicitation by default.
• Any auto-accept mode is explicit and documented.
• Tests cover a server elicitation request that must not be accepted by default.
• Relevant typecheck/test command is run and recorded in the fixing PR.