MCP `pulls` with no repo answers every open pull you can read, with verdict and why it sits; a pull's comments are one read #7655

Part of #7640. The pile is one read, not a loop over repositories.

Done when:

• [ ] pulls without repo answers open pulls across the repositories the caller may read, oldest first, each with repo, number, title, latest check and review verdict, and the gate holding it (from the why module)
• [ ] Paged with next_cursor; a private repository the caller cannot read is absent (test)
• [ ] bun test test/mcp-size.test.ts passes
• [ ] A pull's comments are one GET (/api/v1/repos/:owner/:name/issues/:number/comments for a pull number, proven by a test, or a pulls route) and MCP pull carries them, an outsider's untrusted

Files: src/http/mcp/tools/pulls.ts, src/core/pulls.ts, src/http/mcp/tools/pull.ts, test/mcp-pulls-pile.test.ts

Risks: Answer under 50 ms with 300 open pulls: one query, no per-pull git.

Fits: a builder