feat(skill-creator): leverage Monitor tool for streaming eval progress

**Problem** When /skill-creator runs its eval loop (`run_loop.py`), the entire loop blocks in a single Bash call. The user sees nothing for minutes while 5 iterations of 10+ eval queries run in parallel. This is especially painful for description optimization where each iteration takes 30-60 seconds. **Proposed Solution** Use the new `Monitor` tool to stream eval progress as live notifications. `run_loop.py` already prints per-iteration progress to stderr in verbose mode: ``` Iteration 2/5 Train: 8/10 correct, precision=90% recall=80% accuracy=85% (42.3s) [PASS] rate=3/3 expected=True: write a feature file [FAIL] rate=0/3 expected=True: generate step definitions Best score: 9/10 (iteration 3) ``` The SKILL.md would use Monitor instead of Bash to run the loop: ``` Monitor( command: "python3 run_loop.py --verbose ... 2>&1 | grep -E --line-buffered 'Iteration|Train:|Test :|\\[PASS\\]|\\[FAIL\\]|Best score|Exit reason|Improving|Proposed'", description: "skill-creator eval loop progress" ) ``` **Benefits** 1. User sees live progress instead of waiting for the full batch 2. Agent context is freed during eval runs — can prepare improvement prompts or explain results as they stream in 3. Failure is visible immediately (a crashloop or hung eval shows up as a notification, not as silence) **Implementation Notes** - `run_loop.py` prints progress to stderr, so the Monitor command needs `2>&1` to merge streams - The grep filter should cover both success and failure signals per Monitor best practices - The final JSON output goes to stdout (not stderr), so Monitor won't capture it — the agent reads `results.json` after the Monitor exits - Consider adding a `--progress` flag to `run_loop.py` that prints machine-readable one-line summaries to stdout (instead of relying on stderr + grep)