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 Deleted superseded core/index-doc.md (old pi-era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

omp-docs/skills/ecosystem.md

@@ -0,0 +1,77 @@
+---
+type: reference
+title: Skills Ecosystem
+description: "Registries and the leaderboard API for the open agent-skills ecosystem, with a live-verified install snapshot."
+tags:
+  - skills
+  - skills-sh
+  - ecosystem
+  - registry
+timestamp: 2026-10-19
+verified: 2026-10-19
+---
+
+# Skills Ecosystem
+
+The open agent-skills ecosystem is a set of registries over the shared
+[Agent Skills standard](/skills/agent-skills.md), installed with the
+[Skills CLI](/skills/skills-cli.md).
+
+## Registries
+
+| Registry | Focus |
+|----------|-------|
+| [skills.sh](https://skills.sh) | Primary registry and all-time install leaderboard. |
+| [agentskill.sh](https://agentskill.sh) | Broad directory/marketplace. |
+| [officialskills.sh](https://officialskills.sh) | Skills from major organizations. |
+| [qaskills.sh](https://qaskills.sh) | QA and testing skills. |
+
+## skills.sh leaderboard API
+
+Fetch the all-time ranking programmatically:
+
+```bash
+curl 'https://skills.sh/api/skills/all-time/0'
+```
+
+Response is `{ skills, total, hasMore, page }`. Pagination is **zero-based**,
+**200 skills per page** (`GET /api/skills/all-time/{page}`). Each entry carries
+`source`, `skillId`, `name`, `installs`, `weeklyInstalls` (last ~8 weeks), and
+`isOfficial`. Verified live 2026-10-19: page 0 returned 200 entries,
+`total` 9909, `hasMore` true.
+
+## Install snapshot (2026-10-19, live)
+
+Top 10 by all-time installs, queried from the API above:
+
+| # | Skill | Source | Installs |
+|---|-------|--------|----------|
+| 1 | `find-skills` | vercel-labs/skills | 3,927,274 |
+| 2 | `grill-me` | mattpocock/skills | 1,387,557 |
+| 3 | `grill-with-docs` | mattpocock/skills | 1,188,473 |
+| 4 | `agent-browser` | vercel-labs/agent-browser | 1,170,738 |
+| 5 | `improve-codebase-architecture` | mattpocock/skills | 1,133,991 |
+| 6 | `tdd` | mattpocock/skills | 1,110,148 |
+| 7 | `hyperframes-cli` | heygen-com/hyperframes | 1,109,284 |
+| 8 | `hyperframes` | heygen-com/hyperframes | 1,063,942 |
+| 9 | `setup-matt-pocock-skills` | mattpocock/skills | 1,024,734 |
+| 10 | `handoff` | mattpocock/skills | 1,008,869 |
+
+`mattpocock/skills` dominates the workflow/design middle of the board; a single
+`find-skills` out-installs the next several combined. Vendor suites (Lark, Azure)
+that filled ranks 12-50 in the 2026-08-12 snapshot have since dropped out of the
+head, so this page keeps only a live top-10 rather than a full 50-row table that
+rots between queries. Re-query the API above for a current census.
+
+## Repositories
+
+- [vercel-labs/skills](https://github.com/vercel-labs/skills) — the CLI.
+- [vercel-labs/agent-skills](https://github.com/vercel-labs/agent-skills) — reference skills.
+- [anthropics/skills](https://github.com/anthropics/skills) — Anthropic's skill set.
+- [openai/skills](https://github.com/openai/skills) — OpenAI's skill set.
+
+## See Also
+
+- [The Agent Skills Standard](/skills/agent-skills.md)
+- [Skills CLI](/skills/skills-cli.md)
+- [Skill Store Wiring](/skills/store-wiring.md)