Bump muted/dim text contrast and block label legibility

- --color-text-muted #71717a -> #8b8b96 (~4.9:1 on surface)
- --color-text-dim #52525b -> #6e6e78 (~3.3:1, decorative-only text)
- .block-item-label 10px -> 11px, .block-item-icon 18px -> 20px for
  hierarchy in the Blocks panel tile grid

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/styles/editor.css

@@ -16,8 +16,8 @@
   --color-border: #2d2d3a;
   --color-border-light: #3f3f46;
   --color-text: #e4e4e7;
-  --color-text-muted: #71717a;
-  --color-text-dim: #52525b;
+  --color-text-muted: #8b8b96;
+  --color-text-dim: #6e6e78;
   --color-accent: #3b82f6;
   --color-accent-hover: #2563eb;
   --color-accent-subtle: rgba(59, 130, 246, 0.12);
@@ -704,7 +704,7 @@ body {
 }
 
 .block-item-icon {
-  font-size: 18px;
+  font-size: 20px;
   color: var(--color-text-muted);
   transition: color var(--transition-fast);
 }
@@ -714,7 +714,7 @@ body {
 }
 
 .block-item-label {
-  font-size: 10px;
+  font-size: 11px;
   font-weight: 500;
   color: var(--color-text-muted);
   text-align: center;