Build out the trainer role

is_trainer was captured at signup and stored, but nothing in the app
used it - no client roster, no way to assign anything, a dead flag that
misled users who checked it during registration.

Adds a trainer/client link (a trainer adds a client by the email they
registered with) and lets a trainer create workouts directly on a
client's account (assigned_by_trainer_id on workouts). Deliberately
scoped for privacy: a trainer only ever sees/manages the workouts they
authored and assigned - not a client's other private data (their own
workouts, weight log, health notes, session/completion history). That
boundary needs a consent or notification system to relax safely, which
doesn't exist yet, so it's left for a follow-up rather than building it
half-safe.

WorkoutController's authorization now distinguishes "manage" (owner or
assigning trainer - view, add/edit exercises) from "own" (owner only -
delete), so a trainer can build out an assigned workout's exercises
after creating it, but can't delete a client's workout out from under
them.

Found a real bug via live testing before committing: the client roster
page eager-loaded `assignedWorkouts` (keyed by assigned_by_trainer_id)
on each client record, which is the trainer's own perspective, not the
client's - so it silently showed "no workouts assigned" even after
assigning one. Fixed to eager-load `workouts` filtered by
assigned_by_trainer_id instead, with a regression test.

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

app/Http/Controllers/WorkoutController.php

@@ -17,7 +17,7 @@ class WorkoutController extends Controller
 
     public function index()
     {
-        $workouts = Auth::user()->workouts()->latest()->paginate(10);
+        $workouts = Auth::user()->workouts()->with('assignedByTrainer')->latest()->paginate(10);
         return view('workouts.index', compact('workouts'));
     }
 
@@ -41,7 +41,7 @@ class WorkoutController extends Controller
     public function show(Workout $workout)
     {
         $this->authorizeWorkout($workout);
-        $workout->load(['items.exercise']);
+        $workout->load(['items.exercise', 'assignedByTrainer']);
         $exercises = Exercise::orderBy('name')->limit(20)->get(['id','name','slug']);
         return view('workouts.show', compact('workout', 'exercises'));
     }
@@ -112,15 +112,25 @@ class WorkoutController extends Controller
 
     public function destroy(Workout $workout)
     {
-        $this->authorizeWorkout($workout);
+        // Deletion stays strictly owner-only, even for a trainer-assigned workout.
+        if ($workout->user_id !== Auth::id()) {
+            abort(403);
+        }
         $workout->delete();
         return redirect()->route('workouts.index')->with('status', 'Workout deleted');
     }
 
+    // Allows the owner, or the trainer who assigned this workout, to view and edit it.
+    // Session/completion data is intentionally not exposed to the trainer here - only
+    // the workout structure they authored.
     protected function authorizeWorkout(Workout $workout): void
     {
-        if ($workout->user_id !== Auth::id()) {
-            abort(403);
+        if ($workout->user_id === Auth::id()) {
+            return;
         }
+        if ($workout->assigned_by_trainer_id && $workout->assigned_by_trainer_id === Auth::id()) {
+            return;
+        }
+        abort(403);
     }
 }