fix: add height:100% to all views missing it — eliminates top gap

Views with contain:layout in shadow DOM need explicit height:100%
on :host so their internal flex layout fills the parent's flex
space. Without it, the component doesn't know its height and the
internal content doesn't stretch to fill the panel.

Added height:100% to: cover-grid, artists-view, genres-view,
playlist-view, track-list, config-page (also box-sizing).
explore-view and detail views already had it.

frontend/src/components/artists-view/artists-view.ts

@@ -224,6 +224,7 @@ export class ArtistsView
                 display: flex;
                 flex-direction: column;
                 overflow: hidden;
+                height: 100%;
                 position: relative;
                 contain: layout style;
             }

frontend/src/components/config-page/config-page.ts

@@ -386,6 +386,8 @@ export class ConfigPage extends LitElement {
         :host {
             display: block;
             padding: 1.5em;
+            height: 100%;
+            box-sizing: border-box;
             color: var(--yj-text-primary, #fff);
             font-family: system-ui, -apple-system, sans-serif;
             overflow-y: auto;

frontend/src/components/cover-grid/cover-grid-styles.ts

@@ -8,6 +8,7 @@ const gridStyles = css`
         display: flex;
         flex-direction: column;
         overflow: hidden;
+        height: 100%;
         position: relative;
         contain: layout style;
     }

frontend/src/components/genres-view/genres-view.ts

@@ -229,6 +229,7 @@ export class GenresView
             display: flex;
             flex-direction: column;
             overflow: hidden;
+            height: 100%;
             position: relative;
             contain: layout style;
         }

frontend/src/components/playlist-view/playlist-view.ts

@@ -176,6 +176,7 @@ export class PlaylistView extends LitElement {
             display: flex;
             flex-direction: column;
             overflow: hidden;
+            height: 100%;
             position: relative;
             contain: layout style;
         }

frontend/src/components/track-list/track-list.ts

@@ -747,6 +747,7 @@ export class TrackList extends LitElement implements SelectionHost, ContextMenuH
       display: flex;
       flex-direction: column;
       overflow: hidden;
+      height: 100%;
       contain: layout style;
     }