feat: Sensing-only UI mode with Gaussian splat visualization and Rust migration ADR

- Add Python WebSocket sensing server (ws_server.py) with ESP32 UDP CSI
  and Windows RSSI auto-detect collectors on port 8765
- Add Three.js Gaussian splat renderer with custom GLSL shaders for
  real-time WiFi signal field visualization (blue→green→red gradient)
- Add SensingTab component with RSSI sparkline, feature meters, and
  motion classification badge
- Add sensing.service.js WebSocket client with reconnect and simulation fallback
- Implement sensing-only mode: suppress all DensePose API calls when
  FastAPI backend (port 8000) is not running, clean console output
- ADR-019: Document sensing-only UI architecture and data flow
- ADR-020: Migrate AI/model inference to Rust with RuVector ONNX Runtime,
  replacing ~2.7GB Python stack with ~50MB static binary
- Add ruvnet/ruvector as upstream remote for RuVector crate ecosystem

Co-Authored-By: claude-flow <ruv@ruv.net>

ui/services/api.service.js

@@ -67,9 +67,14 @@ export class ApiService {
   // Generic request method
   async request(url, options = {}) {
     try {
+      // In sensing-only mode, skip all DensePose API calls
+      if (backendDetector.sensingOnlyMode) {
+        throw new Error('DensePose API unavailable (sensing-only mode)');
+      }
+
       // Process request through interceptors
       const processed = await this.processRequest(url, options);
-      
+
       // Determine the correct base URL (real backend vs mock)
       let finalUrl = processed.url;
       if (processed.url.startsWith(API_CONFIG.BASE_URL)) {
@@ -99,7 +104,10 @@ export class ApiService {
       return data;
 
     } catch (error) {
-      console.error('API Request Error:', error);
+      // Only log if not a connection refusal (expected when DensePose API is down)
+      if (error.message && !error.message.includes('Failed to fetch')) {
+        console.error('API Request Error:', error);
+      }
       throw error;
     }
   }