Replace capped exercise picker with a real search combobox

The workout builder's "add exercise" dropdown was Exercise::orderBy
('name')->limit(50) with no search. Harmless with a handful of seeded
exercises, but once the library is populated with real data (1000+),
users could only ever add exercises starting around A-D - the core
"build a workout" flow would be effectively broken.

Replaces it with a debounced Alpine.js combobox backed by a new
GET /workouts/{workout}/exercises/search endpoint (owner-only, JSON,
capped at 20 results, respects each user's custom exercise aliases).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/Http/Controllers/WorkoutController.php

@@ -42,10 +42,26 @@ class WorkoutController extends Controller
     {
         $this->authorizeWorkout($workout);
         $workout->load(['items.exercise']);
-        $exercises = Exercise::orderBy('name')->limit(50)->get(['id','name','slug']);
+        $exercises = Exercise::orderBy('name')->limit(20)->get(['id','name','slug']);
         return view('workouts.show', compact('workout', 'exercises'));
     }
 
+    public function searchExercises(Request $request, Workout $workout)
+    {
+        $this->authorizeWorkout($workout);
+        $q = trim((string) $request->query('q', ''));
+
+        $exercises = Exercise::query()
+            ->with(['aliases' => fn ($rel) => $rel->where('user_id', Auth::id())])
+            ->when($q !== '', fn ($qb) => $qb->where('name', 'like', "%{$q}%"))
+            ->orderBy('name')
+            ->limit(20)
+            ->get(['id', 'name'])
+            ->map(fn ($e) => ['id' => $e->id, 'name' => $e->display_name]);
+
+        return response()->json($exercises);
+    }
+
     // Legacy builder route -> redirect to create
     public function builder()
     {