feat(showcase): add Show button to NSFW notice in main media area

- Add showcase__nsfw-notice-content wrapper for better layout
- Add showcase__nsfw-show-btn with styling matching card.css show-content-btn
- Add show-content action handler that triggers global blur toggle
- Button uses blue accent color with eye icon and hover effects
- Clicking Show button syncs with blur toggle button icon state
- Use unique class names to avoid conflicts with card.css

static/css/base.css

@@ -65,6 +65,8 @@ body {
     --space-1: calc(8px * 1);
     --space-2: calc(8px * 2);
     --space-3: calc(8px * 3);
+    --space-4: calc(8px * 4);
+    --space-5: calc(8px * 5);
 
     /* Z-index Scale */
     --z-base: 10;