Add single-switch scan

New "Scan Switch" header button reuses the Test Connection picker and
posts to /api/scan/switch, which runs the normal scan pipeline on one
switch from the NocoDB inventory. Like a dept scan it does not clear
links first, so the rest of the map is left in place.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scanner.py

@@ -39,10 +39,12 @@ def request_abort():
     return False
 
 
-def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3):
+def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3, only_ip: str = None):
     """
     Full scan: fetch switch IPs from NocoDB → SSH all → parse → store → export.
     dept: None = all active switches, "ELEC" or "GW" = dept-filtered.
+    only_ip: scan just that one switch from the list; like a dept scan, it
+    leaves every other switch's links in place.
     """
     global scan_state
 
@@ -54,6 +56,8 @@ def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3):
 
     # Fetch switch list from NocoDB (or fallback)
     switches = get_switches(dept=dept)
+    if only_ip:
+        switches = [s for s in switches if s["ip"] == only_ip]
 
     if not switches:
         logger.error("NocoDB returned no switches — aborting scan.")
@@ -72,13 +76,13 @@ def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3):
         "fail": 0,
         "errors": [],
         "log_lines": [],
-        "dept_filter": dept,
+        "dept_filter": dept or only_ip,
         "aborted": False,
     })
 
     scan_id = log_scan_start()
-    if dept is None:
-        clear_links()  # Full scan only — dept scans upsert without wiping other depts
+    if dept is None and only_ip is None:
+        clear_links()  # Full scan only — dept/single-switch scans upsert without wiping the rest
 
     def on_progress(done, total, ip, result):
         from datetime import datetime