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

app/web/routes/main.py

@@ -7,7 +7,7 @@ Provides dashboard and scan viewing pages.
 import logging
 import os
 
-from flask import Blueprint, current_app, redirect, render_template, send_from_directory, url_for
+from flask import Blueprint, current_app, redirect, render_template, request, send_from_directory, url_for
 
 from web.auth.decorators import login_required
 
@@ -83,6 +83,19 @@ def compare_scans(scan_id1, scan_id2):
     return render_template('scan_compare.html', scan_id1=scan_id1, scan_id2=scan_id2)
 
 
+@bp.route('/search/ip')
+@login_required
+def search_ip():
+    """
+    IP search results page - shows scans containing a specific IP address.
+
+    Returns:
+        Rendered search results template
+    """
+    ip_address = request.args.get('ip', '').strip()
+    return render_template('ip_search_results.html', ip_address=ip_address)
+
+
 @bp.route('/schedules')
 @login_required
 def schedules():