feat: add GPS status endpoint and dashboard indicator

- add /api/gps/status for thread/fix-age visibility
- surface GPS status in Pi health and live GPS cards
- add tests for app_gps status snapshots

Co-authored-by: Copilot <[email protected]>

templates/index.html

@@ -87,6 +87,11 @@
                 <div class="text-uppercase text-muted fw-bold text-xs mb-1">Uptime</div>
                 <div id="pi-uptime" class="h6 text-dark fw-bold mb-0">--</div>
             </div>
+            <div class="col-6 col-lg-3">
+                <div class="text-uppercase text-muted fw-bold text-xs mb-1">GPS</div>
+                <div id="pi-gps-status" class="h6 text-dark fw-bold mb-0">--</div>
+                <div id="pi-gps-detail" class="small text-muted">Waiting…</div>
+            </div>
         </div>
     </div>
 </div>
@@ -97,9 +102,12 @@
         <div class="card shadow-sm h-100">
             <div class="card-header py-2 d-flex justify-content-between align-items-center">
                 <h6 class="text-primary fw-bold m-0">Live GPS</h6>
-                <button id="btn-recenter" class="btn btn-outline-secondary btn-sm" type="button" title="Recenter map" hidden>
-                    <i class="fas fa-crosshairs" aria-hidden="true"></i>
-                </button>
+                <div class="d-flex align-items-center gap-2">
+                    <span id="gps-live-badge" class="badge text-bg-secondary">Checking…</span>
+                    <button id="btn-recenter" class="btn btn-outline-secondary btn-sm" type="button" title="Recenter map" hidden>
+                        <i class="fas fa-crosshairs" aria-hidden="true"></i>
+                    </button>
+                </div>
             </div>
             <div class="card-body p-0">
                 <div id="map"></div>
@@ -116,6 +124,7 @@
                     </div>
                 </div>
                 <div id="gps-location-name" class="text-muted small" style="font-size:0.75rem;min-height:1rem"></div>
+                <div id="gps-fix-detail" class="text-muted small mt-1" style="font-size:0.75rem;min-height:1rem">Waiting for GPS status…</div>
             </div>
         </div>
     </div>