Mark pull_request_review_write and sub_issue_write as destructive

[JuggerGrimrod88]

What

Sets DestructiveHint: true on the two remaining method-dispatched write tools whose delete/remove method discards data:

• pull_request_review_write — method: "delete_pending" deletes a pending review and discards its body.
• sub_issue_write — method: "remove" deletes a sub-issue link.

Why

This completes the convention established by #2836 (issue #2723) for label_write, and already followed by discussion_comment_write and projects_write: a method-dispatched write tool capable of destruction sets DestructiveHint: true so MCP clients that gate on the hint surface a confirmation prompt before running it.

Before this PR, a client gating on DestructiveHint would warn before label_write delete but not before pull_request_review_write method: "delete_pending" or sub_issue_write method: "remove", even though both discard data. The granular equivalents already flag these as destructive:

• delete_pending_pull_request_review (pkg/github/pullrequests_granular.go) sets DestructiveHint: true.
• remove_sub_issue (pkg/github/issues_granular.go) sets DestructiveHint: true.

So this brings the umbrella method-dispatched tools in line with both their granular equivalents and the sibling umbrella tools (discussion_comment_write, projects_write, label_write). No new judgment call — just consistency.

This was surfaced by a self-review of #2836/#2837: the #2836 rationale ("method-dispatched tools capable of destruction should set DestructiveHint") is satisfied by these two tools as well, so a maintainer would reasonably ask "why only label_write?" — this answers it.

Changes

• pkg/github/pullrequests.go — add DestructiveHint: jsonschema.Ptr(true) to pull_request_review_write (gofmt re-aligned the struct fields).
• pkg/github/issues.go — add DestructiveHint: jsonschema.Ptr(true) to sub_issue_write.
• pkg/github/pullrequests_test.go, pkg/github/issues_test.go — add require.NotNil + assert.True assertions mirroring labels_test.go.
• Regenerated golden snapshots: pull_request_review_write.snap, sub_issue_write.snap (only delta is + "destructiveHint": true).

No behavior, schema, or API change.

Overlap with #2837 (heads-up)

#2837 also edits pull_request_review_write's annotation block (its Title string) and regenerates the same pull_request_review_write.snap. This PR and #2837 touch different fields of the same Annotations struct, so the .go merge is clean. The .snap file will conflict if both merge, but it's a one-line regen — whichever merges second just re-runs UPDATE_TOOLSNAPS=true go test ./pkg/github/ -run TestCreateAndSubmitPullRequestReview. Happy to rebase onto whichever lands first if helpful.

Verification

• gofmt -l clean on all touched files.
• go vet ./pkg/github/
• go build ./...
• go test ./pkg/github/ -run 'TestCreateAndSubmitPullRequestReview|TestCreatePendingPullRequestReview|TestSubmitPendingPullRequestReview|TestDeletePendingPullRequestReview|Test_AddSubIssue|Test_RemoveSubIssue|Test_ReprioritizeSubIssue' — green (snapshots regenerated with UPDATE_TOOLSNAPS=true, then re-run without the flag).