fix(dashcam): add missing dash-col CSS rules, correct MOV mime type and range clamp

- yaris.css: add dash-col-size/date/upload hide rules on mobile (<576px),
  dash-col-file truncation on tablet, btn-icon-mobile label hide
- app.py: clamp byte2 to file_size-1 to prevent Content-Length mismatch;
  detect MIME from file extension (.mov -> video/quicktime)

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

static/yaris.css

@@ -147,8 +147,8 @@ body {
 
 .main-content {
     flex: 1;
-    /* on mobile, leave room for the bottom nav */
-    padding-bottom: 5rem;
+    padding-top: 1.5rem;
+    padding-bottom: 7rem; /* mobile: leave room above bottom nav */
 }
 
 /* ── Mobile bottom navigation ─────────────────────────────────────────────── */
@@ -199,7 +199,7 @@ body {
         margin-left: 0 !important;
     }
     .main-content {
-        padding-bottom: 5rem;
+        padding-bottom: 7rem;
     }
 }
 
@@ -269,6 +269,21 @@ body {
 
 /* ── Dashcam / video ─────────────────────────────────────────────────────── */
 
+/* Hide less-important columns on mobile to keep the table usable */
+@media (max-width: 575.98px) {
+    .dash-col-size,
+    .dash-col-date,
+    .dash-col-upload { display: none; }
+}
+@media (max-width: 767.98px) {
+    .dash-col-file { max-width: 8rem; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+}
+/* Icon-only action buttons on mobile */
+@media (max-width: 575.98px) {
+    .btn-icon-mobile .btn-label { display: none; }
+}
+
+
 .local-video-thumbnail {
     width: 8rem;
     aspect-ratio: 16 / 9;