refactor: generic skills build system with auto-discovery (#8)

* refactor: generic skills build system with auto-discovery

- Rename postgres-best-practices-build → skills-build
- Add auto-discovery: scans skills/ for subdirectories with metadata.json
- Build/validate all skills or specific skill with -- argument
- Update root AGENTS.md and CONTRIBUTING.md with new structure
- No configuration needed to add new skills

Usage:
  npm run build                    # Build all skills
  npm run build -- skill-name      # Build specific skill
  npm run validate                 # Validate all skills

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix ci

* more generic impact levels

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

packages/skills-build/package.json

@@ -0,0 +1,18 @@
+{
+	"name": "skills-build",
+	"version": "1.0.0",
+	"type": "module",
+	"author": "Supabase",
+	"license": "MIT",
+	"description": "Generic build system for Supabase agent skills",
+	"scripts": {
+		"build": "tsx src/build.ts",
+		"validate": "tsx src/validate.ts",
+		"dev": "npm run validate && npm run build"
+	},
+	"devDependencies": {
+		"@types/node": "^20.10.0",
+		"tsx": "^4.7.0",
+		"typescript": "^5.3.0"
+	}
+}