feat(studio): theme picker — 4-color brand theme + curated preset swatches

Extends the studio's 2-color palette to the full 4-color brand theme
(accent / secondary / background / text) matching the Remotion SceneColors,
so the studio's colour state maps 1:1 to the scene engine.

- studio-store: add sceneSecondaryColor + sceneTextColor + their setters + an
  applySceneTheme(accent,secondary,background,text) action (sets all four +
  recolours canvas layers: bg→background, overlays→secondary, shapes→accent,
  text→text explicitly); persist both new fields in hydrate + getSceneDataForSave.
- studio-scene-data: carry sceneSecondaryColor + sceneTextColor through
  VideoPersistedSceneData / build / parse (with defaults).
- ColorsCustomTab: 6 one-click theme presets (Warm/Berry/Midnight/Ocean/Sunset/
  Mono) + 4 manual colour inputs + Apply.
- i18n: secondaryColor/textColor/themePresets/applyTheme(+preset) in fa + en.

Verified with `npm run build`. NOTE: the theme persists in scene_data and
recolours the canvas; wiring the 4 colours all the way to a FlexStory render's
saved_shared_colors depends on the studio-svc shared-colour sync (a small
follow-up). Block-FIELD editing remains the Phase 4 follow-up.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

messages/fa.json

@@ -1148,8 +1148,13 @@
       "description": "صداگذاری را مستقیماً از روی متن خود در استودیو بسازید."
     },
     "componentsStudioSidebarColorsCustomTab": {
-      "mainColor": "رنگ اصلی",
-      "additionalColor": "رنگ مکمل",
+      "mainColor": "پس‌زمینه",
+      "additionalColor": "رنگ اصلی",
+      "secondaryColor": "رنگ دوم",
+      "textColor": "رنگ متن",
+      "themePresets": "تم‌ها",
+      "applyThemePreset": "اعمال تم {name}",
+      "applyTheme": "اعمال تم",
       "applyToAllScenes": "اعمال به همه صحنه‌ها"
     },
     "componentsStudioSidebarColorsPalettesTab": {