Add a community workout library

Workouts were private to their owner with no way to browse or copy
another user's - FavoriteController::toggleWorkout even had a comment
anticipating sharing ("users can still favorite others' workouts if
shared later") that was never followed up on.

Adds an is_public flag workouts can be toggled to from their own page,
a /workouts/community browse+search page, and a copy action that
duplicates a public workout (including all its exercises/sets/reps)
into the copier's own library.

Making this work required splitting workout authorization into two
tiers: authorizeView() (owner, the assigning trainer, or anyone if the
workout is public - read-only) and the existing authorizeWorkout()
(owner or assigning trainer - can add/edit/remove exercises). Deletion
stays strictly owner-only as before. The show page now hides the
"Add Exercise" panel and per-exercise edit/remove controls for viewers
who can see but not manage a workout.

Found and fixed a real Blade compiler quirk via live testing: `@if`
directly after a word character with no space (`exercises@if(...)`)
doesn't compile - Blade's directive regex treats it as email-like text
and leaves it literal - while the matching `@endif` still compiles,
producing invalid mismatched PHP. Fixed by adding a space.

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

resources/views/workouts/index.blade.php

@@ -6,7 +6,10 @@
                     <h1 class="text-2xl sm:text-3xl font-extrabold tracking-tight text-gray-900 dark:text-white">{{ __('app.workouts.my_workouts') }}</h1>
                     <p class="mt-2 text-gray-600 dark:text-gray-300">{{ __('app.workouts.manage_desc') }}</p>
                 </div>
-                <a href="{{ route('workouts.create') }}" class="inline-flex items-center rounded-xl bg-gradient-to-r from-fuchsia-600 to-indigo-600 px-4 py-2 text-sm font-semibold text-white shadow hover:from-fuchsia-500 hover:to-indigo-500">{{ __('app.workouts.new_workout') }}</a>
+                <div class="flex items-center gap-3">
+                    <a href="{{ route('workouts.community') }}" class="inline-flex items-center rounded-xl bg-gray-100 dark:bg-gray-800 px-4 py-2 text-sm font-semibold text-gray-900 dark:text-gray-100 ring-1 ring-gray-200 dark:ring-gray-700 hover:bg-gray-200 dark:hover:bg-gray-700">Browse Community</a>
+                    <a href="{{ route('workouts.create') }}" class="inline-flex items-center rounded-xl bg-gradient-to-r from-fuchsia-600 to-indigo-600 px-4 py-2 text-sm font-semibold text-white shadow hover:from-fuchsia-500 hover:to-indigo-500">{{ __('app.workouts.new_workout') }}</a>
+                </div>
             </div>
         </div>
     </section>