Update ExercisePickerModal to Enforce Backend Suggestion Limit

- Introduced a constant `PLANNING_SUGGEST_LIMIT` set to 50 to align with backend constraints for exercise suggestions.
- Updated the API request limit in `ExercisePickerModal` to utilize the new constant, ensuring compliance with backend specifications.

frontend/src/components/ExercisePickerModal.jsx

@@ -27,6 +27,8 @@ import {
 } from '../utils/exerciseAiQuickCreate'
 
 const PAGE_SIZE = 100
+/** Backend POST /api/planning/exercise-suggest erlaubt max. 50 */
+const PLANNING_SUGGEST_LIMIT = 50
 const LEVEL_FILTER_OPTS = SKILL_LEVEL_OPTIONS.filter((o) => o.level != null)
 
 const INITIAL_FILTERS = { ...INITIAL_EXERCISE_LIST_FILTERS }
@@ -358,7 +360,7 @@ export default function ExercisePickerModal({
           include_llm_rank: Boolean(query),
           query,
           intent_hint: activePlanningContext.intentHint || (useFreePlanningSearch && query ? 'free_search' : null),
-          limit: PAGE_SIZE,
+          limit: PLANNING_SUGGEST_LIMIT,
           exercise_kind_any:
             Array.isArray(exerciseKindAny) && exerciseKindAny.length > 0 ? exerciseKindAny : undefined,
         }