Reject unknown MCP tool arguments before dispatch

[deverman]

Closes #143

Acceptance journey

A client that sends top-level list_tasks.search receives list_tasks.search is unsupported; use list_tasks.filter.search before FocusRelay queries OmniFocus. Unknown nested query and mutation properties likewise fail with their complete argument path.

Validation impact

server-wire

Changes

• derive runtime unknown-property validation from the same schemas returned by tools/list
• recursively close every object schema with additionalProperties: false
• validate before query or mutation dispatch
• add direct JSON-RPC wire coverage for both observed OpenCode payloads plus nested filter, page, and mutation properties
• document the fail-closed MCP boundary

Validation

• swift run focusrelay-dev validate --impact server-wire — 162 tests passed and production build succeeded
• direct wire regression confirms malformed mutation arguments return before performMutation / Bridge dispatch