feat(mcp): add non-sensitive elicitation for planning choices

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Parent roadmap: #127
Parent phase: #234

Goal

Use non-sensitive elicitation for planning choices so MCP clients can ask for missing context without asking for secrets or private identity data.

Requirements

• Ask only for safe planning choices such as repo, contribution lane, time horizon, risk appetite, and whether to prefer cleanup-first work.
• Never ask for tokens, wallet, hotkey, coldkey, private keys, secrets, or private maintainer evidence.
• Make elicitation optional; non-supporting clients must still work with defaults and explicit CLI/tool inputs.
• Keep outputs deterministic and auditable.

Acceptance criteria

• Elicitation requests are allowlisted by field and purpose.
• Unsupported clients keep working without degraded core functionality.
• Sensitive-field attempts are blocked by tests.
• Public output remains sanitized.

Validation expected

• MCP elicitation request fixtures.
• Unsupported-client fallback tests.
• Sensitive-field denylist tests.
• npm run test:ci.