fix(dashboard): leggibilità code block JSON config con syntax highlighting custom

Background code più chiaro (#1A1A24) e font 13.5px line-height 1.6 per
leggibilità migliore.

Override token highlight.js coordinati con palette neon:
- .hljs-attr (chiavi JSON) → cyan #00D9FF
- .hljs-string (valori stringa) → green #00E676
- .hljs-number, .hljs-literal (numeri/bool/null) → pink #FF2D87
- .hljs-keyword, .hljs-built_in → amber #FFB800
- .hljs-punctuation, .hljs-meta → muted #7A7A8C

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/dashboard/nicegui_app.py

@@ -229,13 +229,23 @@ body, .q-page-container, .q-page {{
     margin-bottom: 8px !important;
 }}
 
-code, pre {{
-    background: #0F0F15 !important;
+code, pre, .nicegui-code {{
+    background: #1A1A24 !important;
     color: {COLOR_TEXT} !important;
     border: 1px solid {COLOR_BORDER};
     border-radius: 10px !important;
-    padding: 14px !important;
+    padding: 16px !important;
+    font-size: 13.5px !important;
+    line-height: 1.6 !important;
 }}
+.hljs {{ background: transparent !important; color: {COLOR_TEXT} !important; }}
+.hljs-attr, .hljs-attribute {{ color: {COLOR_SECONDARY} !important; font-weight: 500; }}
+.hljs-string {{ color: {COLOR_SUCCESS} !important; }}
+.hljs-number, .hljs-literal {{ color: {COLOR_PRIMARY} !important; font-weight: 500; }}
+.hljs-keyword, .hljs-built_in {{ color: {COLOR_ACCENT} !important; }}
+.hljs-punctuation, .hljs-meta {{ color: {COLOR_TEXT_MUTED} !important; }}
+.hljs-comment {{ color: {COLOR_TEXT_MUTED} !important; font-style: italic; }}
+.hljs-name, .hljs-title {{ color: {COLOR_PRIMARY} !important; }}
 
 .q-badge {{ border-radius: 6px !important; font-weight: 500 !important; padding: 4px 10px !important; font-size: 12px !important; }}
 </style>