feat(sfm): add SFM proxy router and event data page

- backend/routers/sfm.py: HTTP proxy to SFM backend (localhost:8200),
  mirrors the SLMM proxy pattern. SFM_BASE_URL env var for docker-compose.
  Catch-all /{path} forwards to SFM root (no /api/ prefix). 60s timeout.

- templates/sfm.html: full SFM dashboard with 5 tabs:
  Events (DB listing, filters by serial/date/false-trigger, flag/unflag FT),
  Units (known serials + stats, filter events by unit),
  Monitor Log (continuous monitoring intervals),
  ACH Sessions (call-home history),
  Live Device (TCP connect, device info cards, start/stop monitoring,
  push project config, download events from device, operation log).

- backend/main.py: import sfm router, include router, add GET /sfm route
- templates/base.html: add SFM Live Data nav link under Seismographs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/base.html

@@ -122,6 +122,12 @@
                     </svg>
                     Seismographs
                 </a>
+                <a href="/sfm" class="flex items-center px-4 py-3 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-700 {% if request.url.path == '/sfm' %}bg-gray-100 dark:bg-gray-700{% endif %}">
+                    <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
+                </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 %}">
                     <svg class="w-5 h-5 mr-3" fill="none" stroke="currentColor" viewBox="0 0 24 24">