refactor(sfm): drop ACH/monitor/live-device UI; scope SFM tab to watcher-forwarded events

The /sfm page was originally designed around a Python ACH-server
replacement that would land call-home sessions, monitor-log intervals,
and live-device control alongside triggered events. That work is
paused — deployment uses Blastware's official ACH server and series3-
watcher forwards events to SFM's /db/import/blastware_file. The
sessions/monitor-log/live-device surfaces have no path to populate
under this architecture and were rendering 0/0 everywhere.

Removed (UI only — SFM backend untouched):
- KPI tiles "Monitor Intervals" + "ACH Sessions" (always 0 under
  watcher-forward pipeline)
- Tabs Monitor Log / ACH Sessions / Live Device + their loaders
- Units card columns total_monitor_entries + total_sessions
- Orphaned helpers fmtDuration / fmtBytes
- Live-device state vars + status poll timer
- Subtitle and empty-state copy updated to match reality
- Sidebar: "SFM Live Data" -> "SFM Events"

SFM-side code (ach_sessions/monitor_log tables, /db/sessions,
/db/monitor_log, /device/* endpoints, protocol RE library) is
preserved intact — re-surfacing the tabs later is a UI-only revert.
backend/routers/sfm.py catch-all proxy unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

templates/base.html

@@ -126,7 +126,7 @@
                     <svg class="w-5 h-5 mr-3" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                         <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M13 10V3L4 14h7v7l9-11h-7z"></path>
                     </svg>
-                    SFM Live Data
+                    SFM Events
                 </a>
 
                 <a href="/sound-level-meters" class="flex items-center px-4 py-3 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-700 {% if request.url.path == '/sound-level-meters' %}bg-gray-100 dark:bg-gray-700{% endif %}">