fix: permissions, temp file prefix, session ID extraction

- Fix recommended permissions: add missing Write(/tmp/codex-prompt-*),
  remove overbroad rm rule (cleanup is best-effort)
- Rename claude-plan-* → codex-plan-* so all temp files share codex-* prefix
- Extract session ID via Read tool instead of grep (no extra permission needed)
- Add UUID format spec for session ID validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -98,10 +98,8 @@ permission prompts. To avoid repeated confirmations, add these to your
       "Bash(git symbolic-ref*)",
       "Bash(git rev-parse*)",
       "Bash(timeout 600 codex exec *)",
-      "Bash(rm -f /tmp/claude-plan-*)",
-      "Bash(rm -f /tmp/codex-review-*)",
-      "Write(/tmp/claude-plan-*)",
-      "Write(/tmp/codex-review-*)"
+      "Write(/tmp/codex-plan-*)",
+      "Write(/tmp/codex-prompt-*)"
     ]
   }
 }