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/tsconfig.json

@@ -0,0 +1,16 @@
+{
+	"compilerOptions": {
+		"target": "ES2022",
+		"module": "ESNext",
+		"moduleResolution": "bundler",
+		"esModuleInterop": true,
+		"strict": true,
+		"skipLibCheck": true,
+		"outDir": "dist",
+		"rootDir": "src",
+		"declaration": true,
+		"resolveJsonModule": true
+	},
+	"include": ["src/**/*"],
+	"exclude": ["node_modules", "dist"]
+}