chore: remove device-agent-embedded submodule + update android-agent ref + README

- .gitmodules: remove device-agent-embedded entry (moved to reference/esp32-agent/)

- README.md: add Android Agent and ESP32 Agent to component list, update file structure

- apps/android-agent: update submodule ref (gRPC lifecycle + UI overhaul)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

README.md

@@ -7,7 +7,8 @@ This suite contains four main components:
 1. **[Server Core](http://git.datadunia.com/nexusguard/nexus-server-core)**: The central API and VPN Hub managing database state, token distribution, and Linux firewall isolation.
 2. **[Dashboard UI](http://git.datadunia.com/nexusguard/nexus-dashboard-ui)**: The Admin Web GUI for managing Nodes, Users, Devices, and Firewall rules. Features a futuristic glassmorphism design system using Vue 3, Vite, TailwindCSS v4, and HeadlessUI.
 3. **[Device Agent](http://git.datadunia.com/nexusguard/nexus-device-agent)**: A stealth background daemon for Linux/Windows/macOS client machines that establishes memory-injected WireGuard tunnels.
-4. **[Device Agent Embedded](http://git.datadunia.com/nexusguard/nexus-agent-embedded)**: ESP32-based WireGuard agent for IoT/edge devices. Runs on FreeRTOS + ESP-IDF with lwIP stack.
+4. **[Android Agent](http://git.datadunia.com/nexusguard/nexus-android-agent)**: Android-based WireGuard client for mobile devices using VPNService.
+5. **ESP32 Agent**: Architecture reference only (see `reference/esp32-agent/`).
 
 ---
 
@@ -265,7 +266,10 @@ NexusGuard/
 ├── apps/
 │   ├── server-core/        # Go/Gin API backend
 │   ├── dashboard-ui/       # Vue 3 frontend
-│   └── device-agent/       # Go client agent
+│   ├── device-agent/       # Go client agent
+│   └── android-agent/      # Kotlin Android agent
+├── reference/
+│   └── esp32-agent/        # ESP32 architecture docs (not code)
 ├── bin/                    # Built binaries (gitignored)
 ├── docker-compose.yml      # Docker orchestration
 ├── docker-compose.dev.yml  # Docker dev (hot-reload)