README updates and minor visual fixes

pi/ui/lib/README.md

@@ -22,11 +22,29 @@ All services use singleton pattern with `ServiceName.instance`.
 | Service | Role |
 |---------|------|
 | `ConfigService` | Loads `config.json`, exposes settings |
-| `PiIO` | Pi hardware interface (CPU temp, future GPIO) |
+| `WebSocketService` | socket.io client, streams for arduino/gps/connection/debug, auto-reconnect |
+| `PiIO` | Pi hardware interface (CPU temp) |
 | `OverheatMonitor` | Polls temp, fires callback when threshold exceeded |
 | `ThemeService` | Dark/bright mode state, notifies listeners |
 | `TestFlipFlopService` | Debug: toggles theme + navigator emotion every 2s |
 
+## Key Widgets
+
+| Widget | Purpose |
+|--------|---------|
+| `NavigatorWidget` | Animated character with emotion states (images precached at startup) |
+| `AccelGraph` | Real-time accelerometer visualization with gravity compensation |
+| `WhiskeyMark` | Gimbal-style horizon indicator using IMU roll/pitch |
+| `SystemBar` | Top status bar (time, connection, Pi temp) |
+| `StatBox` | Reusable metric display box |
+| `DebugConsole` | Scrolling log overlay for diagnostics |
+
+## Notes
+
+- **Gravity compensation**: Accelerometer display subtracts 1g from Z-axis to show deviation from vertical
+- **Navigator precaching**: All navigator images are loaded during splash screen to prevent frame drops
+- **Theme switching**: Backend sends `theme_switch` via WebSocket status events (triggered by GPIO)
+
 ## Theme System
 
 - `AppColors` — static color constants (dark/bright variants), auto-generated from JSON

pi/ui/lib/widgets/accel_graph.dart

@@ -151,7 +151,7 @@ class _AccelGraphState extends State<AccelGraph> {
 
             // Label
             Text(
-              'ACCEL',
+              'Acceleration',
               style: TextStyle(
                 fontSize: fontSize * 0.8,
                 fontWeight: FontWeight.w400,
@@ -167,7 +167,9 @@ class _AccelGraphState extends State<AccelGraph> {
 
   String _formatAccel(double? force) {
     if (force == null) return '—°';
-    return '${force.toStringAsFixed(1)}G';
+    return '${
+      force.toStringAsFixed(1) == '-0.0' ? '0.0' : force.toStringAsFixed(1)
+      }G';
   }
 }
 

pi/ui/lib/widgets/whiskey_mark.dart

@@ -85,7 +85,7 @@ class WhiskeyMark extends StatelessWidget {
 
             // Label
             Text(
-              'ATTITUDE',
+              'Attitude',
               style: TextStyle(
                 fontSize: fontSize * 0.8,
                 fontWeight: FontWeight.w400,