fix: make systemd service portable across machines

- Add start-proxy.sh wrapper that handles nvm/fnm/volta/asdf
- Add install-service.sh for one-command installation
- Remove hardcoded node version paths from service file

docs/antigravity-claude-proxy.service

@@ -2,9 +2,10 @@
 #
 # Installation:
 #   1. Copy this file to ~/.config/systemd/user/antigravity-claude-proxy.service
-#   2. Edit the paths below to match your system (especially if using nvm)
-#   3. Run: systemctl --user daemon-reload
-#   4. Run: systemctl --user enable --now antigravity-claude-proxy
+#   2. Copy start-proxy.sh to a permanent location (e.g., ~/.local/bin/)
+#   3. Update PROXY_SCRIPT below to point to start-proxy.sh
+#   4. Run: systemctl --user daemon-reload
+#   5. Run: systemctl --user enable --now antigravity-claude-proxy
 #
 # Management:
 #   systemctl --user status antigravity-claude-proxy
@@ -20,10 +21,9 @@ After=network.target
 Type=simple
 # Customize the port as needed
 Environment=PORT=3001
-# Update PATH to include your node binary location (check with: which node)
-Environment=PATH=%h/.nvm/versions/node/v22.14.0/bin:/usr/local/bin:/usr/bin:/bin
-# Update this path to match your antigravity-claude-proxy location (check with: which antigravity-claude-proxy)
-ExecStart=%h/.nvm/versions/node/v22.14.0/bin/antigravity-claude-proxy start
+# Path to the wrapper script - update this to match your installation
+# The wrapper script handles nvm/fnm/volta/asdf automatically
+ExecStart=%h/.local/bin/start-proxy.sh start
 Restart=on-failure
 RestartSec=5