Add IP address search feature with global search box

- Add API endpoint GET /api/scans/by-ip/{ip_address} to retrieve
  last 10 scans containing a specific IP
- Add ScanService.get_scans_by_ip() method with ScanIP join query
- Add search box to global navigation header
- Create dedicated search results page at /search/ip
- Update API documentation with new endpoint

docs/API_REFERENCE.md

@@ -989,6 +989,56 @@ curl -X DELETE http://localhost:5000/api/scans/42 \
   -b cookies.txt
 ```
 
+### Get Scans by IP
+
+Get the last 10 scans containing a specific IP address.
+
+**Endpoint:** `GET /api/scans/by-ip/{ip_address}`
+
+**Authentication:** Required
+
+**Path Parameters:**
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `ip_address` | string | Yes | IP address to search for |
+
+**Success Response (200 OK):**
+```json
+{
+  "ip_address": "192.168.1.10",
+  "scans": [
+    {
+      "id": 42,
+      "timestamp": "2025-11-14T10:30:00Z",
+      "duration": 125.5,
+      "status": "completed",
+      "title": "Production Network Scan",
+      "config_id": 1,
+      "triggered_by": "manual",
+      "created_at": "2025-11-14T10:30:00Z"
+    },
+    {
+      "id": 38,
+      "timestamp": "2025-11-13T10:30:00Z",
+      "duration": 98.2,
+      "status": "completed",
+      "title": "Production Network Scan",
+      "config_id": 1,
+      "triggered_by": "scheduled",
+      "created_at": "2025-11-13T10:30:00Z"
+    }
+  ],
+  "count": 2
+}
+```
+
+**Usage Example:**
+```bash
+curl -X GET http://localhost:5000/api/scans/by-ip/192.168.1.10 \
+  -b cookies.txt
+```
+
 ### Compare Scans
 
 Compare two scans to identify differences in ports, services, and certificates.