docs(skills): collapse three overlapping skills trees into one verified tree

Three parallel trees documented the same ecosystem: omp-docs/skills/
(two overview pages), tools/npx-skills/ (10 pi-era npm pages), and
tools/vercel-labs-skills/ (11 CLI pages), plus a fourth leaderboard page
at engineering/skills-ecosystem.md. Verbatim overlap (identical SKILL.md
field tables in skills-spec.md vs skill-format.md; 13-agent vs 68-agent
copies of the same upstream table). Consolidated to four concept pages:

- skills/agent-skills.md: standard, format, loading, authoring (merges
  skills-spec, skill-format, skill-file-structure, skill-loading,
  best-practices, skills-vs-extensions)
- skills/skills-cli.md: CLI reference (merges commands, source-formats,
  installation-scope, skill-discovery, lock-file, env-variables,
  agent-support, related-links)
- skills/store-wiring.md: moved, fleet ops, links retargeted
- skills/ecosystem.md: replaces skills-ecosystem.md; stale 2026-08-12
  top-50 table dropped, replaced with a live top-10 re-queried from the
  skills.sh API tonight and the API contract re-verified (zero-based,
  200/page, {skills,total,hasMore,page}, total 9909)

All facts re-verified 2026-10-19 against primary sources:
agentskills.io, vercel-labs/skills README + src/cli.ts (command set,
--full-depth) + src/skill-lock.ts (v3 lock, XDG path, wipe-on-old),
live skills.sh API. Deleted superseded core/index-doc.md (old pi-era
docs index). Retargeted all inbound links (tools/index, engineering x3,
packages x3, pi/skills, core/index). Pi-era npm skill packaging is
listed as archived under /pi/.

Refs #29

scripts/kb-lint.sh

@@ -7,6 +7,7 @@ KB="$(cd "${1:-omp-docs}" 2>/dev/null && pwd)" || { echo "kb-lint: no such dir:
 
 python3 - "$KB" <<'PY'
 import re, sys
+import yaml
 from pathlib import Path
 kb = Path(sys.argv[1])
 violations = []
@@ -14,6 +15,7 @@ violations = []
 for p in sorted(kb.rglob("*.md")):
     rel = p.relative_to(kb)
     text = p.read_text(errors="replace")
+    lines = text.splitlines()
     if p.name == "index.md":
         # OKF rule: index files are directory listings and carry NO frontmatter.
         if text.startswith("---"):
@@ -22,9 +24,18 @@ for p in sorted(kb.rglob("*.md")):
     if not text.startswith("---"):
         violations.append(f"{rel}: missing frontmatter")
         continue
-    end = text.find("\n---", 3)
-    fm = text[3:end] if end != -1 else ""
-    if not re.search(r"^type:", fm, re.M):
+    # Close the block at the first line that is exactly --- or ...; anything
+    # else (including fenced `---` deep in the body) is body, not a delimiter.
+    end = next((i for i in range(1, len(lines)) if lines[i].strip() in ("---", "...")), None)
+    if end is None:
+        violations.append(f"{rel}: frontmatter block is not closed (no '---' delimiter line)")
+        continue
+    try:
+        fm = yaml.safe_load("\n".join(lines[1:end])) or {}
+    except yaml.YAMLError:
+        violations.append(f"{rel}: frontmatter block is malformed YAML or not closed")
+        continue
+    if not isinstance(fm, dict) or not str(fm.get("type", "")).strip():
         violations.append(f"{rel}: frontmatter lacks required 'type:'")
 
 # link integrity: fenced code blocks hold example paths, not live links — strip first.