fix(skills): validate bundled SKILL.md front-matter in CI (fixes #2443) (#2457)

* fix(skills): validate bundled SKILL.md front-matter in CI (fixes #2443)

Adds a parametrized backend test that runs `_validate_skill_frontmatter`
against every bundled SKILL.md under `skills/public/`, so a broken
front-matter fails CI with a per-skill error message instead of
surfacing as a runtime gateway-load warning.

The new test caught two pre-existing breakages on `main` and fixes them:

* `bootstrap/SKILL.md`: the unquoted description had a second `:` mid-line
  ("Also trigger for updates: ..."), which YAML parses as a nested mapping
  ("mapping values are not allowed here"). Rewrites the description as a
  folded scalar (`>-`), which preserves the original wording (including the
  embedded colon, double quotes, and apostrophes) without further escaping.
  This complements PR #2436 (single-file colon→hyphen patch) with a more
  general convention that survives future edits.

* `chart-visualization/SKILL.md`: used `dependency:` which is not in
  `ALLOWED_FRONTMATTER_PROPERTIES`. Renamed to `compatibility:`, the
  documented field for "Required tools, dependencies" per skill-creator.
  No code reads `dependency` (verified by grep across backend/).

* Apply suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Fix the lint error

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

backend/tests/test_skills_bundled.py

@@ -0,0 +1,31 @@
+"""Validate every bundled SKILL.md under skills/public/.
+
+Catches regressions like #2443 — a SKILL.md whose YAML front-matter fails to
+parse (e.g. an unquoted description containing a colon, which YAML interprets
+as a nested mapping). Each bundled skill is checked individually so the
+failure message identifies the exact file.
+"""
+
+from pathlib import Path
+
+import pytest
+
+from deerflow.skills.validation import _validate_skill_frontmatter
+
+SKILLS_PUBLIC_DIR = Path(__file__).resolve().parents[2] / "skills" / "public"
+BUNDLED_SKILL_DIRS = sorted(p.parent for p in SKILLS_PUBLIC_DIR.rglob("SKILL.md"))
+
+
+@pytest.mark.parametrize(
+    "skill_dir",
+    BUNDLED_SKILL_DIRS,
+    ids=lambda p: str(p.relative_to(SKILLS_PUBLIC_DIR)),
+)
+def test_bundled_skill_frontmatter_is_valid(skill_dir: Path) -> None:
+    valid, msg, name = _validate_skill_frontmatter(skill_dir)
+    assert valid, f"{skill_dir.relative_to(SKILLS_PUBLIC_DIR)}: {msg}"
+    assert name, f"{skill_dir.relative_to(SKILLS_PUBLIC_DIR)}: no name extracted"
+
+
+def test_skills_public_dir_has_skills() -> None:
+    assert BUNDLED_SKILL_DIRS, f"no SKILL.md found under {SKILLS_PUBLIC_DIR}"