Publish lean skill market snapshot

Constraint: This repository is a skill distribution snapshot, so download size matters more than historical auditability.
Rejected: Preserve prior Git history | Old large blobs keep clone size high and do not help skill consumers.
Confidence: high
Scope-risk: broad
Directive: Future market updates should be validated, then collapsed to a fresh snapshot commit before push.
Tested: python scripts/validate_marketplace.py; validate_plugin.py plugins/codex/plugins/ppt-master; uv run python -m pytest backend/tests/test_skill_market_publish.py backend/tests/test_skill_market_scheduler.py -q; node web/tests/skills-market-ui.test.mjs; git diff --check; Codex temp install/use test for ppt-master
Not-tested: PowerShell execution because pwsh/powershell is not installed locally.

plugins/codex/README.md

@@ -0,0 +1,24 @@
+# Codex 插件市场目录
+
+这个目录是 EAPIL Codex 插件市场的稀疏安装入口。通常推荐从仓库根目录添加市场，并把稀疏路径留空；只有在需要减少拉取范围时才使用本目录。
+
+从仓库根目录安装市场：
+
+```powershell
+codex plugin marketplace add https://git.playones.com/arechen/EapilSkillMarket.git --ref main
+```
+
+使用稀疏路径安装市场：
+
+```powershell
+codex plugin marketplace add https://git.playones.com/arechen/EapilSkillMarket.git --ref main --sparse .agents --sparse plugins/codex
+```
+
+本地调试：
+
+```powershell
+codex plugin marketplace add .\plugins\codex
+codex plugin add docx@eapil-skill-market
+```
+
+每个 `plugins/<plugin-name>` 目录都是独立插件，用户可以只安装自己需要的插件。插件内可以包含一个或多个相关 Skill。