Add Dangerous Pi MVP implementation - complete backend and system integration

This commit adds the complete Dangerous Pi web management interface with all MVP features implemented and tested locally.

## New Features

### Backend (Python + FastAPI)
- Complete FastAPI backend with async support
- 40+ API endpoints (Health, PM3, WiFi, Updates, UPS, BLE, Plugins)
- 6 managers: Session, WiFi, Update, UPS, BLE, Plugin
- SQLite database with sessions, config, history, crash reports
- Server-Sent Events (SSE) for real-time notifications
- Mock PM3 worker for development without hardware

### WiFi Manager
- Interface detection (USB vs built-in)
- Network scanning with signal strength
- Mode switching (AP/Client/Dual/Auto/Off)
- Network connection with password support
- Hidden SSID and saved networks support
- Static IP and DHCP configuration
- 10 WiFi API endpoints

### Update Manager
- GitHub releases API integration
- Automatic periodic update checks
- Semantic version comparison
- Update download with progress tracking
- SHA256 checksum verification
- Automatic installation with backup and rollback
- PM3 client rebuild after updates
- 6 Update API endpoints

### UPS Manager
- I2C battery monitoring (MAX17040-compatible)
- Battery percentage, voltage, current tracking
- Power source detection (AC/Battery)
- Safe shutdown triggers at configurable thresholds
- Event callbacks for battery warnings
- SSE and BLE notification integration
- 3 UPS API endpoints

### BLE Manager
- Bluetooth Low Energy notification support
- Auto-detects BLE capability
- Multiple notification types (updates, battery, shutdown, etc.)
- BLE advertising management
- Device connection tracking
- 4 BLE API endpoints

### Plugin Framework
- Dynamic plugin loading/unloading
- Plugin lifecycle management (load, enable, disable, unload)
- Hook system for extensibility
- JSON-based metadata
- Example "Hello World" plugin included
- 7 Plugin API endpoints

### Frontend (Remix.js + React)
- Cyberpunk-themed responsive UI
- Dashboard with system status
- PM3 command interface with history
- Settings page with WiFi and Update management
- Command logs viewer
- Theme toggle (Dark/Light/Auto)
- Server-side rendering (SSR)
- Mobile-first responsive design

### System Integration
- Systemd service with security hardening
- Automated install/uninstall scripts
- Environment configuration template
- Hardware access groups (i2c, bluetooth, gpio, dialout)
- Pi-gen stage 04 integration for OS image building
- Port conflict resolution with ttyd-bash
- I2C interface auto-enable for UPS HAT

### Testing
- test_backend.py - Backend API tests
- test_ups.py - UPS manager tests
- test_ble.py - BLE manager tests
- test_plugins.py - Plugin manager tests
- All tests passing locally

### Documentation
- 12 comprehensive documentation files
- claude.md - AI development guide
- WIFI_MANAGER.md - WiFi management guide
- UPDATE_MANAGER.md - Update system guide
- PORT_CONFLICT.md - Port conflict resolution guide
- MVP_COMPLETE.md - MVP implementation summary
- PROJECT_STATUS.md - Project status and roadmap
- systemd/README.md - Service management docs
- pi-gen integration documentation

## Technical Details
- ~5,000+ lines of backend code
- 11 Python dependencies (smbus2 added for UPS)
- FastAPI with async/await throughout
- Type hints and docstrings on all functions
- RESTful API design with SSE for notifications
- Security hardening (non-root, protected dirs, resource limits)

## Next Steps
- Deploy to Raspberry Pi Zero 2 W hardware
- Test with real Proxmark3 device
- Test UPS HAT integration
- Test BLE on Pi hardware
- Build custom OS image with pi-gen
- Performance optimization for Pi Zero 2 W

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/plugins/hello_world/main.py

@@ -0,0 +1,56 @@
+"""Hello World example plugin for Dangerous Pi."""
+import sys
+from pathlib import Path
+
+# Add app directory to path for imports
+app_path = Path(__file__).parent.parent.parent
+if str(app_path) not in sys.path:
+    sys.path.insert(0, str(app_path))
+
+from backend.managers.plugin_manager import PluginBase, PluginMetadata
+
+
+class HelloWorldPlugin(PluginBase):
+    """Example plugin that demonstrates the plugin framework."""
+
+    def __init__(self):
+        """Initialize the Hello World plugin."""
+        super().__init__()
+        self.counter = 0
+
+    async def on_load(self):
+        """Called when the plugin is loaded."""
+        print("Hello World Plugin: Loaded!")
+
+    async def on_enable(self):
+        """Called when the plugin is enabled."""
+        print("Hello World Plugin: Enabled!")
+
+        # Register a hook for PM3 commands
+        async def pm3_command_hook(command: str):
+            """Hook that logs PM3 commands."""
+            self.counter += 1
+            print(f"Hello World Plugin: PM3 command #{self.counter}: {command}")
+            return {"plugin": "hello_world", "command_count": self.counter}
+
+        self.register_hook("pm3_command", pm3_command_hook)
+
+        # Register a hook for update checks
+        async def update_check_hook():
+            """Hook that runs on update checks."""
+            print("Hello World Plugin: Update check performed")
+            return {"plugin": "hello_world", "message": "Hello from plugin!"}
+
+        self.register_hook("update_check", update_check_hook)
+
+    async def on_disable(self):
+        """Called when the plugin is disabled."""
+        print(f"Hello World Plugin: Disabled! (processed {self.counter} commands)")
+
+    async def on_unload(self):
+        """Called when the plugin is unloaded."""
+        print("Hello World Plugin: Unloaded! Goodbye!")
+
+    def get_metadata(self) -> PluginMetadata:
+        """Get plugin metadata."""
+        return self.metadata

app/plugins/hello_world/plugin.json

@@ -0,0 +1,10 @@
+{
+  "id": "hello_world",
+  "name": "Hello World Plugin",
+  "version": "1.0.0",
+  "description": "Example plugin demonstrating the plugin framework",
+  "author": "Dangerous Pi Team",
+  "homepage": "https://github.com/yourusername/dangerous-pi",
+  "dependencies": [],
+  "permissions": []
+}