feat(skills): bulk-add root SKILL.md to 61 skills (native Agent Skills loadability)

Run the additive migration pass from SKILL-MIGRATION-GUIDE: generate a root SKILL.md
for every skill that lacked one, copied from its desktop/SKILL.md (or code/SKILL.md),
with name set to the directory name and description + body preserved verbatim.

- scripts/migrate_skill_root.py: the reusable, non-destructive migrator (dry-run default).
- 61 new root SKILL.md (desktop source for most; code/SKILL.md for 61/62/92).
- Untouched: 16/17/95 (already had root); desktop/ and code/ packaging left intact.
- All 64 root SKILL.md validate: frontmatter <=1024, kebab name, description present.

Still MANUAL (no SKILL.md source — commands/README only), need hand-authored root SKILL.md:
81-mac-optimizer, 90-reference-curator, 91-multi-agent-guide, 94-dintel-bootstrap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/migrate_skill_root.py

@@ -0,0 +1,128 @@
+#!/usr/bin/env python3
+"""
+migrate_skill_root.py — additive bulk migration: give each skill a root SKILL.md.
+
+Non-destructive. For every skill directory under custom-skills/ that lacks a root
+SKILL.md, it generates one by copying the skill's existing directive and:
+  - setting `name:` to the directory name (guaranteed kebab-case + unique),
+  - preserving `description` and the markdown body verbatim,
+  - validating the result (frontmatter <= 1024 chars, kebab name, description present).
+
+Source priority per skill:  desktop/SKILL.md  ->  code/SKILL.md.
+It NEVER touches desktop/, code/, or an existing root SKILL.md.
+
+The implementation of the SKILL-MIGRATION-GUIDE recipe, for the whole repo at once.
+
+Usage:
+  python scripts/migrate_skill_root.py            # dry-run (default): report only
+  python scripts/migrate_skill_root.py --apply    # write the new root SKILL.md files
+"""
+
+import argparse
+import re
+import sys
+from pathlib import Path
+
+REPO = Path(__file__).resolve().parent.parent
+SKILLS = REPO / "custom-skills"
+FM_RE = re.compile(r"^---\n(.*?)\n---\n?(.*)$", re.S)
+MAX_FM = 1024
+
+
+def is_skill_dir(d):
+    """A skill dir is a real skill, not shared infra."""
+    if not d.is_dir():
+        return False
+    n = d.name
+    return not (n.startswith("_") or n.endswith("-shared"))
+
+
+def find_source(d):
+    """Existing directive to copy from, by priority."""
+    for cand in (d / "desktop" / "SKILL.md", d / "code" / "SKILL.md"):
+        if cand.exists():
+            return cand
+    return None
+
+
+def set_name(frontmatter, name):
+    """Replace the single-line `name:` value (or prepend one) with `name`."""
+    if re.search(r"^name:.*$", frontmatter, re.M):
+        return re.sub(r"^name:.*$", f"name: {name}", frontmatter, count=1, flags=re.M)
+    return f"name: {name}\n{frontmatter}"
+
+
+def build_root_skill(src_text, dir_name):
+    """Return (new_skill_text, issues[]) or (None, issues) if unusable."""
+    m = FM_RE.match(src_text)
+    if not m:
+        return None, ["source has no YAML frontmatter"]
+    fm, body = m.group(1), m.group(2).lstrip("\n")
+    fm = set_name(fm, dir_name)
+
+    issues = []
+    if len(fm) > MAX_FM:
+        issues.append(f"frontmatter {len(fm)}>{MAX_FM} chars")
+    if "description:" not in fm:
+        issues.append("no description")
+    if not re.search(r"^name:\s*[a-z0-9-]+\s*$", fm, re.M):
+        issues.append("name not kebab-case")
+
+    text = f"---\n{fm}\n---\n\n{body}"
+    return text, issues
+
+
+def main(argv=None):
+    ap = argparse.ArgumentParser(description="Additively add a root SKILL.md to each skill.")
+    ap.add_argument("--apply", action="store_true", help="write files (default: dry-run)")
+    args = ap.parse_args(argv)
+
+    rows = []  # (dir, status, detail)
+    created = skipped = manual = warned = 0
+
+    for d in sorted(SKILLS.iterdir()):
+        if not is_skill_dir(d):
+            continue
+        name = d.name
+        if (d / "SKILL.md").exists():
+            rows.append((name, "SKIP", "already has root SKILL.md"))
+            skipped += 1
+            continue
+        src = find_source(d)
+        if not src:
+            rows.append((name, "MANUAL", "no desktop/ or code/ SKILL.md source (commands/README only)"))
+            manual += 1
+            continue
+        text, issues = build_root_skill(src.read_text(encoding="utf-8"), name)
+        rel = src.relative_to(d)
+        if text is None:
+            rows.append((name, "MANUAL", f"{rel}: {issues[0]}"))
+            manual += 1
+            continue
+        if issues:
+            rows.append((name, "CREATE*", f"from {rel} | FIX: {'; '.join(issues)}"))
+            warned += 1
+        else:
+            rows.append((name, "CREATE", f"from {rel}"))
+            created += 1
+        if args.apply:
+            (d / "SKILL.md").write_text(text, encoding="utf-8")
+
+    width = max(len(r[0]) for r in rows)
+    print(f"{'SKILL':<{width}}  STATUS   DETAIL")
+    print(f"{'-'*width}  -------  ------")
+    for name, status, detail in rows:
+        print(f"{name:<{width}}  {status:<7}  {detail}")
+
+    mode = "APPLIED" if args.apply else "DRY-RUN (no files written)"
+    print(f"\n[{mode}]  create={created}  create-with-fix={warned}  "
+          f"skip={skipped}  manual={manual}  total_skills={len(rows)}")
+    if warned:
+        print("  * CREATE* rows were written but need a frontmatter fix (see FIX note).")
+    if not args.apply:
+        print("  Re-run with --apply to write the files.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())