fix: revert claude review trigger to pull_request (#2152)

Reverts the pull_request_target trigger back to pull_request.

The pull_request_target trigger was introduced in #2145 to support fork
PRs, but Anthropic's OIDC token exchange endpoint does not accept tokens
from pull_request_target events, causing 100% failure rate on all
reviews since March 9th.

This is a known upstream issue:
anthropics/claude-code-action#713

Until Anthropic adds pull_request_target to their OIDC allowlist, we
revert to pull_request which works for same-repo branch PRs.

Author: viral-sangani

.github/workflows/claude-code-review.yml

@@ -1,7 +1,7 @@
 name: Claude Code Review
 
 on:
-  pull_request_target:
+  pull_request:
     types: [opened, synchronize, ready_for_review, reopened]
     # Optional: Only run on specific file changes
     # paths: