An agent reads a fork family's iterations through an MCP iterations tool, as GET /api/v1/repos/:owner/:name/iterations does #9126

Intent: done means reachable through MCP; an agent in any harness reads the family tree of builds without scraping the page.

Done looks like:

• [x] src/http/mcp/tools/iterations.ts registers an iterations tool taking owner and name, answering what the API route answers for the same caller, through the same module.
• [x] Its doc names every argument and what it answers, as the builds, forks and family tools' docs do (the test from #9110's rule passes).
• [x] A test calls the tool for a readable family, a private repository the caller may not read (not found) and a family with no pins (empty lists).
• [x] llms.txt / the here manifest list the tool where they list builds and family.

Files: one new tool module, the tool index, one test. Risk: none beyond the API's; keep one source of truth.

Reviewed pull #9151 at its head: ticked src/http/mcp/tools/iterations.ts registers an iterations tool taking owner and name, answering what the API route answers for the same caller, through the same module.; Its doc names every argument and what it answers, as the builds, forks and family tools' docs do (the test from #9110's rule passes).; A test calls the tool for a readable family, a private repository the caller may not read (not found) and a family with no pins (empty lists).; llms.txt / the here manifest list the tool where they list builds and family..