Commenting through …/issues/{number}/comments on a pull's number comments on the pull, as the OpenAPI document says #3298

Found 2026-10-20 by the planner: POST /api/v1/repos/trevato/forge/issues/3245/comments answered not_found for pull #3245, while src/contract/openapi.ts describes that route as "Comment on an issue or pull". Only …/pulls/{number}/comments (src/http/api.ts:3817) works for a pull.

Done:

• [ ] The issues comment route (src/http/api.ts, /api/v1/repos/:owner/:name/issues/:number/comments) accepts a pull's number and adds the comment to the pull through the same addCommentThrough path, with the same scope and origin checks.
• [ ] Same answer shape as commenting on an issue; a number that is neither stays not_found.
• [ ] A test in test/ opens a pull, comments on it through the issues route, and reads the comment back on the pull. The test fails without the change.

Files: src/http/api.ts, one test file. Risk: a pull-only rule, such as a sealed or taken-up pull, must still apply. Reuse loadPull; don't copy it. Builder: scout or mason.