fix: clarify pending review creation

[he-yufeng]

Summary

• make the pull_request_review_write title say that create opens a pending review
• clarify that method: "create" without event does not submit the review
• update the tool snapshot and README tool list

Fixes #2524.

To verify

• UPDATE_TOOLSNAPS=true go test ./pkg/github -run TestCreateAndSubmitPullRequestReview -count=1
• go test ./pkg/github -run TestCreateAndSubmitPullRequestReview -count=1
• go test ./pkg/github -count=1
• go test ./...
• git diff --check

[he-yufeng]

Rebased the branch onto current origin/main and force-pushed 5a97566.

Validation after rebase:

• go test ./...

[SamMorrowDrums]

Targeted fix for #2524 — makes it clear that create without event produces a pending review, and refreshes the description to cover all five methods (including resolve_thread/unresolve_thread). README and toolsnap are updated consistently.

Minor nit: the user-facing Title annotation still doesn't mention thread resolve/unresolve, while the description does. Could broaden in a follow-up (e.g. "Manage pull request reviews and review threads"), not blocking. LGTM.