feat(classroom): add TrackDef type and wrap existing modules into core track

Adds TrackDef type to shared/learn/types.ts and creates learnTracks
export in learnModules.ts with existing 4 modules grouped under
'Core Flight Missions' track. Backward compatible — learnModules
flat array still exported.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/data/learnModules.ts

@@ -1,5 +1,5 @@
 import { createBaseScenario, createScenarioSeries, digitsToWords, formatTemp, lettersToNato } from '~~/shared/learn/scenario'
-import type { ModuleDef, Scenario } from '~~/shared/learn/types'
+import type { ModuleDef, Scenario, TrackDef } from '~~/shared/learn/types'
 
 function gradientArt(colors: string[]): string {
   const stops = colors
@@ -3292,4 +3292,13 @@ export const learnModules: ModuleDef[] = [
   }
 ]
 
+export const learnTracks: TrackDef[] = [
+  {
+    id: 'core',
+    title: 'Core Flight Missions',
+    subtitle: 'From basics to full flight',
+    modules: learnModules,
+  },
+]
+
 export default learnModules