feat: port 3 interactive geometry lessons + geom-engine

- Add pure geom-engine module (vec, triangle, circle, ticks) with 34 vitest tests
- Add 3 lessons under /hinh-hoc/: tam-giac-bang-nhau (SSS), tam-giac-dong-dang (similarity), goc-noi-tiep (inscribed angle)
- Add reactive draggable Svelte action with arrow-key a11y
- Add per-lesson colocated i18n + site chrome + lesson registry
- Enable Hình học topic card on landing; keep Số học/Đại số as Sắp ra mắt
- Codify pedagogical tick palette as Tailwind colors.pair.{1,2,3}
- Add Be Vietnam Pro via @fontsource

jsconfig.json

@@ -1,14 +1,7 @@
 {
+  "extends": "./.svelte-kit/tsconfig.json",
   "compilerOptions": {
-    "moduleResolution": "bundler",
-    "target": "ESNext",
-    "module": "ESNext",
     "checkJs": true,
-    "allowJs": true,
-    "paths": {
-      "$lib": ["src/lib"],
-      "$lib/*": ["src/lib/*"]
-    }
-  },
-  "include": ["src/**/*", ".svelte-kit/ambient.d.ts", ".svelte-kit/types/**/$types.d.ts"]
+    "allowJs": true
+  }
 }