feat: Migrate from Socket.IO to Server-Sent Events (SSE)

- Replace Socket.IO with SSE for real-time server-to-client communication
- Add SSE service with client management and topic-based subscriptions
- Implement SSE authentication middleware and streaming endpoints
- Update all backend routes to emit SSE events instead of Socket.IO
- Create SSE context provider for frontend with EventSource API
- Update all frontend components to use SSE instead of Socket.IO
- Add comprehensive SSE tests for both backend and frontend
- Remove Socket.IO dependencies and legacy files
- Update documentation to reflect SSE architecture

Benefits:
- Simpler architecture using native browser EventSource API
- Lower bundle size (removed socket.io-client dependency)
- Better compatibility with reverse proxies and load balancers
- Reduced resource usage for Raspberry Pi deployment
- Standard HTTP-based real-time communication

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

backend/middleware/sseAuth.js

@@ -0,0 +1,42 @@
+const jwt = require("jsonwebtoken");
+
+/**
+ * SSE Authentication Middleware
+ * Supports token from query string (for SSE connections) or Authorization header
+ */
+module.exports = function (req, res, next) {
+  let token;
+
+  // Try to get token from query string (for SSE EventSource connections)
+  if (req.query.token) {
+    token = req.query.token;
+  }
+  // Try to get token from Authorization header (Bearer token)
+  else if (req.headers.authorization && req.headers.authorization.startsWith("Bearer ")) {
+    token = req.headers.authorization.substring(7);
+  }
+  // Try to get token from x-auth-token header (legacy support)
+  else if (req.header("x-auth-token")) {
+    token = req.header("x-auth-token");
+  }
+
+  // Check if no token found
+  if (!token) {
+    return res.status(401).json({ 
+      success: false, 
+      msg: "No token, authorization denied" 
+    });
+  }
+
+  // Verify token
+  try {
+    const decoded = jwt.verify(token, process.env.JWT_SECRET);
+    req.user = decoded.user;
+    next();
+  } catch (err) {
+    return res.status(401).json({ 
+      success: false, 
+      msg: "Token is not valid" 
+    });
+  }
+};