feat: add npx installer CLI

- Add package.json with bin for antigravity-awesome-skills
- Add bin/install.js: clone to ~/.agent/skills (default), --cursor/--claude/--gemini/--path
- Git pull if dir exists; core.symlinks=true on Windows
- Update README and GETTING_STARTED with npx instructions

package.json

@@ -0,0 +1,24 @@
+{
+  "name": "antigravity-awesome-skills",
+  "version": "4.0.0",
+  "description": "560+ agentic skills for Claude Code, Gemini CLI, Cursor, Antigravity & more. Installer CLI.",
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/sickn33/antigravity-awesome-skills.git"
+  },
+  "bin": {
+    "antigravity-awesome-skills": "./bin/install.js"
+  },
+  "files": [
+    "bin"
+  ],
+  "keywords": [
+    "claude-code",
+    "cursor",
+    "gemini-cli",
+    "antigravity",
+    "agentic-skills",
+    "ai-coding"
+  ]
+}