Reject unsupported pagination params in pull_request_read

[muhammadumer-waheed]

Summary

pull_request_read now returns a validation error when a pagination parameter is passed that the selected method does not use, instead of silently dropping it.

Why

A pagination parameter that the selected method cannot honour was silently dropped: an agent following the schema and passing after to e.g. get_files would get the first page back again with no signal that anything was ignored. Silent parameter drops are worst-case for agentic callers, since the tool reports success with a plausible payload and the model has no reason to retry.

Fixes #3316

What changed

• Added validatePaginationParamsForMethod in pkg/github/pullrequests.go, called before the tool dispatches on method:
  • after is rejected for all methods except get_review_comments (with a hint to use get_review_comments for cursor-based pagination)
  • page is rejected for get_review_comments, which uses cursor-based pagination
  • perPage remains accepted for every method
• Added table-driven tests covering both rejection cases plus positive cases confirming page/perPage still work for get_files and perPage/after still work for get_review_comments.

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

The pull_request_read input schema is unchanged; behavior only: passing a pagination parameter the selected method does not honour now returns an error naming the method and the parameter, instead of silently returning the first page.

Prompts tested (tool changes only)

• "Show me the files changed in PR [docker] build arm64 #42, page 2 with 10 per page" → get_files with page/perPage: accepted (covered by unit test)
• "Get the review comments on PR [docker] build arm64 #42 after cursor cursor-page-2" → get_review_comments with after: accepted (covered by unit test)
• "Get the files changed in PR [docker] build arm64 #42 after cursor cursor-page-2" → get_files with after: now errors with method "get_files" uses page/perPage pagination; "after" is not supported (covered by unit test)

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)