feat: asset-based image/video sources, notification sounds, UI improvements

- Replace URL-based image_source/url fields with image_asset_id/video_asset_id
  on StaticImagePictureSource and VideoCaptureSource (clean break, no migration)
- Resolve asset IDs to file paths at runtime via AssetStore.get_file_path()
- Add EntitySelect asset pickers for image/video in stream editor modal
- Add notification sound configuration (global sound + per-app overrides)
- Unify per-app color and sound overrides into single "Per-App Overrides" section
- Persist notification history between server restarts
- Add asset management system (upload, edit, delete, soft-delete)
- Replace emoji buttons with SVG icons throughout UI
- Various backend improvements: SQLite stores, auth, backup, MQTT, webhooks

server/src/wled_controller/static/css/modal.css

@@ -1466,64 +1466,42 @@
     line-height: 1;
 }
 
-/* ── Notification app color mappings ─────────────────────────── */
+/* ── Notification per-app overrides (unified color + sound) ──── */
 
-.notif-app-color-row {
-    display: flex;
+.notif-override-row {
+    display: grid;
+    grid-template-columns: 1fr auto auto auto;
+    gap: 4px 4px;
     align-items: center;
-    gap: 6px;
-    margin-bottom: 4px;
+    margin-bottom: 6px;
+    padding-bottom: 6px;
+    border-bottom: 1px solid var(--border-color);
 }
 
-.notif-app-color-row .notif-app-name {
-    flex: 1;
+.notif-override-row .notif-override-name,
+.notif-override-row .notif-override-sound {
     min-width: 0;
 }
 
-.notif-app-color-row .notif-app-color {
-    width: 28px;
-    height: 28px;
+/* Sound select spans the first column, volume spans browse+color columns */
+.notif-override-row .notif-override-sound {
+    grid-column: 1;
+}
+.notif-override-row .notif-override-volume {
+    grid-column: 2 / 4;
+    width: 100%;
+}
+
+.notif-override-row .notif-override-color {
+    width: 26px;
+    height: 26px;
     border: 1px solid var(--border-color);
     border-radius: 4px;
     padding: 1px;
     cursor: pointer;
     background: transparent;
-    flex-shrink: 0;
 }
 
-.notif-app-browse,
-.notif-app-color-remove {
-    background: none;
-    border: 1px solid var(--border-color);
-    color: var(--text-muted);
-    border-radius: 4px;
-    cursor: pointer;
-    padding: 0;
-    width: 28px;
-    height: 28px;
-    min-width: unset;
-    display: inline-flex;
-    align-items: center;
-    justify-content: center;
-    flex-shrink: 0;
-    transition: border-color 0.2s, color 0.2s;
-}
-
-.notif-app-browse svg {
-    width: 14px;
-    height: 14px;
-}
-
-.notif-app-color-remove {
-    font-size: 0.75rem;
-    line-height: 1;
-}
-
-.notif-app-browse:hover,
-.notif-app-color-remove:hover {
-    border-color: var(--primary-color);
-    color: var(--text-color);
-}
 
 /* ── Notification history list ─────────────────────────────────── */
 
@@ -1866,3 +1844,128 @@ body.composite-layer-dragging .composite-layer-drag-handle {
     opacity: 0 !important;
 }
 
+/* ── File drop zone ── */
+.file-dropzone {
+    position: relative;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 8px;
+    padding: 28px 20px;
+    border: 2px dashed var(--border-color);
+    border-radius: var(--radius-md);
+    background: var(--bg-color);
+    cursor: pointer;
+    transition: border-color var(--duration-normal) ease,
+                background var(--duration-normal) ease,
+                box-shadow var(--duration-normal) ease;
+    user-select: none;
+    outline: none;
+}
+
+.file-dropzone:hover {
+    border-color: var(--primary-color);
+    background: color-mix(in srgb, var(--primary-color) 5%, var(--bg-color));
+}
+
+.file-dropzone:focus-visible {
+    border-color: var(--primary-color);
+    box-shadow: 0 0 0 3px rgba(76, 175, 80, 0.15);
+}
+
+.file-dropzone.dragover {
+    border-color: var(--primary-color);
+    border-style: solid;
+    background: color-mix(in srgb, var(--primary-color) 10%, var(--bg-color));
+    box-shadow: 0 0 0 3px rgba(76, 175, 80, 0.15),
+                inset 0 0 20px rgba(76, 175, 80, 0.06);
+}
+
+.file-dropzone.has-file {
+    border-style: solid;
+    border-color: var(--primary-color);
+    padding: 16px 20px;
+}
+
+.file-dropzone-icon {
+    color: var(--text-muted);
+    transition: color var(--duration-normal) ease, transform var(--duration-normal) var(--ease-spring);
+}
+
+.file-dropzone:hover .file-dropzone-icon,
+.file-dropzone.dragover .file-dropzone-icon {
+    color: var(--primary-color);
+    transform: translateY(-2px);
+}
+
+.file-dropzone.has-file .file-dropzone-icon {
+    color: var(--primary-color);
+}
+
+.file-dropzone-text {
+    text-align: center;
+}
+
+.file-dropzone-label {
+    font-size: 0.9rem;
+    color: var(--text-muted);
+    transition: color var(--duration-normal) ease;
+}
+
+.file-dropzone:hover .file-dropzone-label {
+    color: var(--text-secondary);
+}
+
+.file-dropzone-info {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    padding: 6px 12px;
+    border-radius: var(--radius-sm);
+    background: var(--bg-secondary);
+    width: 100%;
+    max-width: 100%;
+    overflow: hidden;
+}
+
+.file-dropzone-filename {
+    flex: 1;
+    font-size: 0.88rem;
+    font-weight: var(--weight-medium);
+    color: var(--text-color);
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+}
+
+.file-dropzone-filesize {
+    font-size: 0.8rem;
+    color: var(--text-muted);
+    white-space: nowrap;
+    font-family: var(--font-mono);
+}
+
+.file-dropzone-remove {
+    flex-shrink: 0;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: 22px;
+    height: 22px;
+    border: none;
+    border-radius: var(--radius-sm);
+    background: transparent;
+    color: var(--text-muted);
+    font-size: 1.1rem;
+    cursor: pointer;
+    transition: background var(--duration-fast) ease, color var(--duration-fast) ease;
+    line-height: 1;
+    padding: 0;
+}
+
+.file-dropzone-remove:hover {
+    background: var(--danger-color);
+    color: white;
+}
+