draw every kind of textbook figure, lock math text left-to-right, student-first family screen

- src/diagram: plane (constructed points, graphs with computed roots, vertex,
  extrema, tangent, asymptotes, piecewise limits, regions, rotations and
  reflections, line from ax + by = c), number line with intervals and stacked
  fractions, solids with hidden edges, bar/line/pie charts, sign tables, Venn,
  arrow mappings, probability trees, fraction bars and mixed numbers, grids,
  groups, clock. Pure-math text is bidi-overridden: Persian digits used to turn
  3 × 4 = 12 into 12 = 4 × 3 even with dir=ltr.
- MathText locks math runs inside Persian sentences in chat bubbles and figure
  captions, so -1 no longer shows as 1-.
- Family screen: a student sees only the invite-code form; the parent form is
  behind a link.
- Dev-only diagram gallery at ?gallery (not in the production build).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.tsx

@@ -1,10 +1,20 @@
-import { StrictMode } from 'react';
+import { StrictMode, lazy, Suspense } from 'react';
 import { createRoot } from 'react-dom/client';
 import { App } from './app/App';
 import './styles/index.css';
 
+// گالریِ شکل‌ها فقط در حالتِ توسعه؛ در build اصلاً وارد نمی‌شود (import.meta.env.DEV ثابت است).
+const DiagramGallery = import.meta.env.DEV
+  ? lazy(() => import('./dev/DiagramGallery').then((m) => ({ default: m.DiagramGallery })))
+  : null;
+const showGallery = DiagramGallery && new URLSearchParams(window.location.search).has('gallery');
+
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <App />
+    {showGallery && DiagramGallery ? (
+      <Suspense fallback={null}><DiagramGallery /></Suspense>
+    ) : (
+      <App />
+    )}
   </StrictMode>,
 );