Add GitHub metadata enrichment for catalog apps

Enrich catalog apps with GitHub API data (stars, version, downloads,
release date) via two strategies: background drip for repo-level info
and on-demand fetch when opening a detail page.

- Add github_enrichment module with API calls, asset filtering, and
  architecture auto-detection for AppImage downloads
- DB migrations v14/v15 for GitHub metadata and release asset columns
- Extract github_owner/repo from feed links during catalog sync
- Display colored stat cards (stars, version, downloads, released) on
  detail pages with on-demand enrichment
- Show stars and version on browse tiles and featured carousel cards
- Replace install button with SplitButton dropdown when multiple arch
  assets available, preferring detected architecture
- Disable install button until enrichment completes to prevent stale
  AppImageHub URL downloads
- Keep enrichment banner visible on catalog page until truly complete,
  showing paused state when rate-limited
- Add GitHub token and auto-enrich toggle to preferences

data/app.driftwood.Driftwood.gschema.xml

@@ -142,5 +142,15 @@
       <summary>Watch removable media</summary>
       <description>Scan removable drives for AppImages when mounted.</description>
     </key>
+    <key name="github-token" type="s">
+      <default>''</default>
+      <summary>GitHub personal access token</summary>
+      <description>Optional GitHub token for higher API rate limits (5,000 vs 60 requests per hour).</description>
+    </key>
+    <key name="catalog-auto-enrich" type="b">
+      <default>true</default>
+      <summary>Auto-enrich catalog apps</summary>
+      <description>Automatically fetch GitHub metadata (stars, version, downloads) for catalog apps in the background.</description>
+    </key>
   </schema>
 </schemalist>

data/resources/style.css

@@ -175,6 +175,53 @@ button.flat:not(.pill):not(.suggested-action):not(.destructive-action) {
     min-height: 24px;
 }
 
+/* ===== Catalog Tile Cards ===== */
+.catalog-tile {
+    border: 1px solid alpha(@window_fg_color, 0.12);
+    border-radius: 12px;
+}
+
+.catalog-tile:hover {
+    border-color: alpha(@accent_bg_color, 0.5);
+}
+
+/* ===== Featured Banner Cards ===== */
+.catalog-featured-card {
+    border-radius: 12px;
+    border: 1px solid alpha(@window_fg_color, 0.15);
+    padding: 0;
+}
+
+.catalog-featured-card:hover {
+    border-color: alpha(@accent_bg_color, 0.5);
+}
+
+/* Screenshot area inside featured card */
+.catalog-featured-screenshot {
+    border-radius: 11px 11px 0 0;
+    border: none;
+    background: alpha(@window_fg_color, 0.04);
+}
+
+.catalog-featured-screenshot picture {
+    border-radius: 11px 11px 0 0;
+}
+
+/* ===== Destructive Context Menu Item ===== */
+.destructive-context-item {
+    color: @error_fg_color;
+    background: alpha(@error_bg_color, 0.85);
+    border: none;
+    box-shadow: none;
+    padding: 6px 12px;
+    border-radius: 6px;
+    min-height: 28px;
+}
+
+.destructive-context-item:hover {
+    background: @error_bg_color;
+}
+
 /* ===== Screenshot Lightbox ===== */
 window.lightbox {
     background-color: rgba(0, 0, 0, 0.92);
@@ -193,3 +240,75 @@ window.lightbox .lightbox-nav {
     min-width: 48px;
     min-height: 48px;
 }
+
+/* ===== Catalog Tile Stats Row ===== */
+.catalog-stats-row {
+    font-size: 0.8em;
+    color: alpha(@window_fg_color, 0.7);
+}
+
+.catalog-stats-row image {
+    opacity: 0.65;
+}
+
+/* ===== Detail Page Stat Cards ===== */
+.stat-card {
+    background: alpha(@window_fg_color, 0.06);
+    border-radius: 12px;
+    padding: 14px 16px;
+    border: 1px solid alpha(@window_fg_color, 0.08);
+}
+
+.stat-card.stat-stars {
+    background: alpha(@warning_bg_color, 0.12);
+    border-color: alpha(@warning_bg_color, 0.2);
+}
+
+.stat-card.stat-stars image {
+    color: @warning_bg_color;
+    opacity: 0.85;
+}
+
+.stat-card.stat-version {
+    background: alpha(@accent_bg_color, 0.1);
+    border-color: alpha(@accent_bg_color, 0.18);
+}
+
+.stat-card.stat-version image {
+    color: @accent_bg_color;
+    opacity: 0.85;
+}
+
+.stat-card.stat-downloads {
+    background: alpha(@success_bg_color, 0.1);
+    border-color: alpha(@success_bg_color, 0.18);
+}
+
+.stat-card.stat-downloads image {
+    color: @success_bg_color;
+    opacity: 0.85;
+}
+
+.stat-card.stat-released {
+    background: alpha(@purple_3, 0.12);
+    border-color: alpha(@purple_3, 0.2);
+}
+
+.stat-card.stat-released image {
+    color: @purple_3;
+    opacity: 0.85;
+}
+
+.stat-card .stat-value {
+    font-weight: 700;
+    font-size: 1.15em;
+}
+
+.stat-card .stat-label {
+    font-size: 0.8em;
+    color: alpha(@window_fg_color, 0.6);
+}
+
+.stat-card image {
+    opacity: 0.55;
+}