feat(media): add reusable MediaPickerComponent

Standalone dialog (app-dialog, size lg) reusing MediaLibraryFacade so it
shares the exact same asset list/search/pagination/upload state as the
Media Manager page. Emits (selected) with the chosen MediaAsset and
(closed) to dismiss - selecting a tile emits both.

Completes Sprint 4 (Media Manager): ADR-0002 contract, MediaRepository +
mock IndexedDB adapter, Media Manager UI, reusable Media Picker.

Not yet wired into Product Editor or Static Pages editor - that's the
next natural step when those features gain image fields, not part of
this sprint's scope.

src/app/shared/media/media-picker/media-picker.component.scss

@@ -0,0 +1,44 @@
+.media-picker {
+  display: grid;
+  gap: 14px;
+}
+
+.media-picker__toolbar {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.media-picker__grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
+  gap: 10px;
+}
+
+.media-picker__preview {
+  width: 100%;
+  height: 90px;
+  object-fit: cover;
+  border-radius: var(--radius-md, 6px);
+  background: var(--bg-secondary, #f4f4f5);
+  margin-bottom: 6px;
+}
+
+.media-picker__preview--file {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 0.6875rem;
+  color: var(--text-secondary, #6b7280);
+  text-align: center;
+  padding: 6px;
+}
+
+.media-picker__filename {
+  display: block;
+  font-size: 0.75rem;
+  color: var(--text-primary, #1f322d);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}