Fix styling issues: dialog backgrounds, spacing tokens, and module category

- Added category 'Audio/Video' to module.json to fix 'Non répertorié' issue
- Created styles/tokens/_spacing.less with spacing tokens (xxs, xs, sm, md, lg, xl, 2xl)
- Added legacy aliases (--sp-space-xs, --sp-space-sm, --sp-space-m, etc.) for preset-import-export.less
- Added --sp-bg and --sp-surface-elevated tokens to _base.less
- Fixed _player-privacy-panel.less to use CSS custom properties instead of LESS variables
- Added background: var(--sp-surface) to all dialog root elements:
  - PlayerPrivacyPanel
  - PresetSaveDialog
  - PresetLoadDialog
  - DirectorsBoard
  - PresetImport/Export dialogs
- Added _spacing.less import to scrying-pool.less
- Rebuilt CSS (dist/styles/scrying-pool.css)

This fixes:
1. Transparent dialogs (now have proper background colors)
2. Missing spacing tokens (caused build errors)
3. Module category (now shows as 'Audio/Video' instead of 'Uncategorized')

All 900 unit tests passing.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

styles/tokens/_base.less

@@ -17,8 +17,10 @@
 
 :root {
   /* Surface & structure */
+  --sp-bg:                 var(--sp-theme-bg,            var(--color-bg,              hsl(220, 15%, 12%)));
   --sp-surface:             var(--sp-theme-surface,       var(--color-bg-option,       #141618));
   --sp-surface-raised:      var(--sp-theme-surface-raised, #1c1f22);
+  --sp-surface-elevated:   var(--sp-theme-surface-elevated, var(--sp-surface-raised, #1c1f22));
   --sp-border:              var(--sp-theme-border,        var(--color-border,          #282c30));
 
   /* Typography */
@@ -45,8 +47,10 @@
 /* Theme overrides — dark theme defaults */
 .scrying-pool,
 :root[data-color-scheme="dark"] {
+  --sp-theme-bg:              hsl(220, 15%, 12%);
   --sp-theme-surface:        #141618;
   --sp-theme-surface-raised: #1c1f22;
+  --sp-theme-surface-elevated: #1c1f22;
   --sp-theme-border:         #282c30;
   --sp-theme-text-primary:   #dde2e8;
   --sp-theme-text-secondary: #7a8390;

styles/tokens/_spacing.less

@@ -0,0 +1,29 @@
+/**
+ * styles/tokens/_spacing.less
+ *
+ * Layer 1 — SP Spacing Tokens
+ *
+ * Semantic spacing tokens for consistent layout.
+ * Maps to Foundry's spacing scale where available.
+ */
+
+:root {
+  --sp-spacing-xxs: 2px;
+  --sp-spacing-xs: 4px;
+  --sp-spacing-sm: 8px;
+  --sp-spacing-md: 12px;
+  --sp-spacing-lg: 16px;
+  --sp-spacing-xl: 24px;
+  --sp-spacing-2xl: 32px;
+  
+  /* Border radius */
+  --sp-border-radius: 4px;
+  --sp-border-radius-lg: 8px;
+  
+  /* Legacy aliases for preset-import-export.less */
+  --sp-space-xs: var(--sp-spacing-xs, 4px);
+  --sp-space-sm: var(--sp-spacing-sm, 8px);
+  --sp-space-m: var(--sp-spacing-md, 12px);
+  --sp-space-l: var(--sp-spacing-lg, 16px);
+  --sp-space-xl: var(--sp-spacing-xl, 24px);
+}