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.

.env.example

@@ -1,5 +1,15 @@
 # Claude Code UI Environment Configuration
 # Only includes variables that are actually used in the code
+#
+# TIP: Run 'cloudcli status' to see where this file should be located
+#      and to view your current configuration.
+#
+# Available CLI commands:
+#   claude-code-ui    - Start the server (default)
+#   cloudcli start    - Start the server
+#   cloudcli status   - Show configuration and data locations
+#   cloudcli help     - Show help information
+#   cloudcli version  - Show version information
 
 # =============================================================================
 # SERVER CONFIGURATION
@@ -19,10 +29,11 @@ VITE_PORT=5173
 # =============================================================================
 
 # Path to the authentication database file
-# This should be set to a persistent volume path when running in containers
-# Default: server/database/auth.db (relative to project root)
-# Example for Docker: /data/auth.db
-# DATABASE_PATH=/data/auth.db
+# This is where user credentials, API keys, and tokens are stored.
+#
+# To use a custom location:
+# DATABASE_PATH=/path/to/your/custom/auth.db
+#
 # Claude Code context window size (maximum tokens per session)
 # Note: VITE_ prefix makes it available to frontend
 VITE_CONTEXT_WINDOW=160000