v0.6.0: MCP tools

Agents can use tools from MCP servers, plus fixes found while moving Clevix to the latest kit. Go module github.com/eadwinCode/agentic-kit/packages/go-agentenkit@v0.6.0, npm agentenkit@0.6.0 and use-agentenkit@0.6.0.

No breaking changes.

MCP tools (#21)

• A small MCP client in both runtimes: agentenkit/adapters/mcp and go-agentenkit/adapters/mcp. It needs no new dependencies.
• It connects over stdio or streamable HTTP and turns each of the server's tools into an ordinary tool.
• Options: a name prefix, a list of tools to keep, approval per tool, and a time limit.
• Tool errors, time limits and a lost server go back to the model as {"error": ...}.
• See the new MCP docs page.

Fixes (#22)

• Refused sends no longer grow the thread. A send refused at dispatch (billing, a full queue) is now sent live only, so a user who keeps pressing Send no longer adds a row to the thread each time. A refusal at pickup belongs to a run and is still stored.
• Admin reads can carry the tenant. rt.Admin.WithState(state) (TS: runtime.admin.withState(state)) lets the reads that go to storage carry the tenant. These are a run's and a thread's spend, and a run's events.
• use-agentenkit:
  • A refused run() returns reason and retryAfterSeconds, from the body or a Retry-After header.
  • It reads { error: { code, message } } bodies.
  • After a reload, a tool call carries its stored result.
  • isToolError reads JSON text and lists of results.
  • isToolParked and toolCallResults are exported.
• isToolUse / IsToolUse tell a paid tool service's usage line from a model call.