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>

database/migrations/2026_08_10_093228_add_is_public_to_workouts_table.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('workouts', function (Blueprint $table) {
+            $table->boolean('is_public')->default(false)->after('title');
+            $table->index('is_public');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('workouts', function (Blueprint $table) {
+            $table->dropIndex(['is_public']);
+            $table->dropColumn('is_public');
+        });
+    }
+};