Add PR progress comment and increase Cursor review timeout.

Post a temporary in-progress comment while reviewing, remove it when done, default timeout to 10 minutes, and skip retries on timeout.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -7,6 +7,6 @@ PORT=8787
 
 DEFAULT_BASE_BRANCH=main
 MAX_INLINE_COMMENTS=5
-REVIEW_TIMEOUT_MS=120000
+REVIEW_TIMEOUT_MS=600000
 DEDUPE_TTL_SECONDS=1800
 LOG_LEVEL=info