serve-cockpit: declare PyYAML dependency (fixes c3 diagnose-estate crash)

c3 shells out to the repo's profile scripts (estate_cli.py, weights.py,
compat.py, …) which `import yaml`. PyYAML was never declared, so a
`uv pip install -e tools/serve-cockpit` venv lacks it — and since c3's
python3 subprocess resolves to that venv interpreter, Doctor → diagnose-estate
died with `ModuleNotFoundError: No module named 'yaml'` (worked on the
maintainer rig only because SYSTEM python3 happened to have it).

Reported by @alexpolo1 (discussions/459). Repro'd in a clean venv (import yaml
fails) → after this fix the editable install resolves yaml and estate_cli.py
report-state/diagnose run clean. PyYAML is the ONLY third-party dep across all
scripts c3 shells out to (rest is stdlib).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EfF565T9eSLaqGzidyJ1Pm

tools/serve-cockpit/pyproject.toml

@@ -12,6 +12,13 @@ dependencies = [
     "club3090-tui-core>=0.1.0",
     "textual>=0.60",
     "rich>=13.0",
+    # The cockpit shells out to the repo's profile scripts (estate_cli.py,
+    # weights.py, compat.py, classifier.py, patch_attribution.py) which
+    # `import yaml`. Declaring PyYAML here means a `uv pip install -e` /
+    # `pip install` venv has it — otherwise `c3`'s python3 subprocess (the
+    # venv interpreter) hits `ModuleNotFoundError: No module named 'yaml'`
+    # on Doctor → diagnose-estate (works only if SYSTEM python3 has it).
+    "pyyaml>=6.0",
 ]
 
 [project.scripts]