feat(mcp): serve the host's schema tools through the MCP facade

[TonsOfFun]

Closes #439. Stacked on #443 (it needs agent_actor); retarget to main once that merges.

#439 asked for a mounted Rack endpoint serving the schema-tool roster over MCP. As the review on #443 noted, Api::MCPController already is that endpoint; what was missing was the roster. This extends the facade rather than adding a second server — one definition, two transports.

Change

• tools/list offers every tool the dashboard's discovered ActiveAgent::SchemaTools classes generate — find_<records>, count_<records>, get_<record> — beside the run_<slug> agents, each with the tool's own parameter schema as inputSchema, so a client sees which columns it may filter on.
• tools/call on one of them runs SchemaTools.call(name, actor: agent_actor, **arguments): the key's caller (or whatever ActionAgent.agent_actor_resolver returns), through the host's own scope, exactly as inside an agent run. Arguments that name the caller (actor, current_user) are dropped, for the reason Carry the caller into agent runs, so agents can authorize like controllers #443 gives.
• A boundary violation (an undeclared filter, an id the caller cannot see) is a tool result with isError, the shape an agent's model would get, so a client can correct its call. A refusal raised by the host's scope — ActiveAgent::NotAuthorized or an error named with denies_with — is a JSON-RPC -32003, as an agent's refusal is.
• No generation runs, so neither execution_enabled nor the execution quota applies to a direct read, and no execution usage is recorded.
• ActionAgent.mcp_schema_tools = false keeps the tools reachable only through agents. On by default: the host declared them, and every key holder could already reach them through any agent that has them enabled.
• autoload :NotAuthorized in lib/active_agent.rb: the class is defined in concerns/authorization.rb, loaded only with Base, and the engine referencing it before any agent class had loaded raised NameError (which run_refused? on Carry the caller into agent runs, so agents can authorize like controllers #443 sidesteps by comparing strings).
• docs/framework/dashboard.md gains a section on the facade; docs/work/schema-tools-follow-ups/ records this batch of work (branches, issues, milestones, PRs).

Testing

• actionagent/test/mcp_schema_tools_test.rb: nine cases — listing beside agents with the parameter schema, running as the resolved caller with the client's arguments, a client cannot name the caller, unattributed when nothing resolves, a boundary violation as isError, a refusal as -32003, unknown tool, the switch, no execution switch or quota.
• bin/test actionagent/test/mcp_*_test.rb test/authorization_test.rb — 30 runs, 83 assertions, 0 failures.
• bin/rubocop clean on the changed files.

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https://claude.ai/code/session_01XMSRnSxYS9mRx1hSjytB9Z