fix: prevent TOCTOU race condition on issue/PR body edits (#710)

Add trigger-time validation for issue/PR body content to prevent attackers
from exploiting a race condition where they edit the body between when an
authorized user triggers @claude and when Claude processes the request.

The existing filterCommentsToTriggerTime() already protected comments -
this extends the same pattern to the main issue/PR body via isBodySafeToUse().

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

src/github/api/queries/github.ts

@@ -13,6 +13,8 @@ export const PR_QUERY = `
         headRefName
         headRefOid
         createdAt
+        updatedAt
+        lastEditedAt
         additions
         deletions
         state
@@ -96,6 +98,8 @@ export const ISSUE_QUERY = `
           login
         }
         createdAt
+        updatedAt
+        lastEditedAt
         state
         comments(first: 100) {
           nodes {