docs: update installation and CLI documentation

Update .env.example with comprehensive CLI command documentation and
clearer DATABASE_PATH configuration comments. Enhance README.md with
restructured installation guide featuring new cloudcli commands,
detailed PM2 background service setup instructions, and improved
organization of global installation benefits and restart procedures.

Add CLI command reference showing cloudcli start, status, help, and
version commands. Expand PM2 section with separate subsections for
installation, service startup, and auto-start configuration.

package.json

@@ -5,7 +5,8 @@
   "type": "module",
   "main": "server/index.js",
   "bin": {
-    "claude-code-ui": "server/index.js"
+    "claude-code-ui": "server/cli.js",
+    "cloudcli": "server/cli.js"
   },
   "files": [
     "server/",