Refactor enrichFrameworkSlotSections to improve section handling in training framework

- Updated the enrichFrameworkSlotSections function to utilize default sections when no sections are provided, enhancing data integrity.
- Simplified the normalization process by directly using base sections, improving code clarity and maintainability.

frontend/src/pages/TrainingFrameworkProgramEditPage.jsx

@@ -48,14 +48,10 @@ function emptySlot() {
 async function enrichFrameworkSlotSections(slots) {
   const out = []
   for (const s of slots || []) {
-    const sec = normalizeUnitToForm({
-      sections: s.sections,
-      exercises: s.exercises,
-      phases: s.phases,
-    })
+    const baseSecs = s.sections && s.sections.length ? s.sections : [defaultSection('Ablauf')]
     out.push({
       ...s,
-      sections: await enrichSectionsWithVariants(sec),
+      sections: await enrichSectionsWithVariants(baseSecs),
     })
   }
   return out