docs: Add comprehensive wifi-Mat user guide and fix compilation

- Add detailed wifi-Mat user guide covering:
  - Installation and setup
  - Detection capabilities (breathing, heartbeat, movement)
  - Localization system (triangulation, depth estimation)
  - START protocol triage classification
  - Alert system with priority escalation
  - Field deployment guide
  - Hardware setup requirements
  - API reference and troubleshooting

- Update main README.md with wifi-Mat section and links

- Fix compilation issues:
  - Add missing deadline field in AlertPayload
  - Fix type ambiguity in powi calls
  - Resolve borrow checker issues in scan_cycle
  - Export CsiDataBuffer from detection module
  - Add missing imports in test modules

- All 83 tests now passing

rust-port/wifi-densepose-rs/crates/wifi-densepose-mat/src/domain/alert.rs

@@ -130,6 +130,7 @@ impl AlertPayload {
             triage_status,
             location: None,
             recommended_action: String::new(),
+            deadline: None,
             metadata: std::collections::HashMap::new(),
         }
     }

rust-port/wifi-densepose-rs/crates/wifi-densepose-mat/src/domain/disaster_event.rs

@@ -289,18 +289,22 @@ impl DisasterEvent {
         location: Option<Coordinates3D>,
     ) -> Result<&Survivor, MatError> {
         // Check if this might be an existing survivor
-        if let Some(loc) = &location {
-            if let Some(existing) = self.find_nearby_survivor(loc, 2.0) {
-                // Update existing survivor
-                let survivor = self.survivors.iter_mut()
-                    .find(|s| s.id() == existing)
-                    .ok_or_else(|| MatError::Domain("Survivor not found".into()))?;
-                survivor.update_vitals(vitals);
-                if let Some(l) = location {
-                    survivor.update_location(l);
-                }
-                return Ok(survivor);
+        let existing_id = if let Some(loc) = &location {
+            self.find_nearby_survivor(loc, 2.0).cloned()
+        } else {
+            None
+        };
+
+        if let Some(existing) = existing_id {
+            // Update existing survivor
+            let survivor = self.survivors.iter_mut()
+                .find(|s| s.id() == &existing)
+                .ok_or_else(|| MatError::Domain("Survivor not found".into()))?;
+            survivor.update_vitals(vitals);
+            if let Some(l) = location {
+                survivor.update_location(l);
             }
+            return Ok(survivor);
         }
 
         // Create new survivor