Add streaks and milestone badges

No gamification existed at all - nothing rewarded consistency or gave
users a reason to come back beyond the raw session stats already on
the dashboard. Adds a Gamification helper that derives (not stores)
a current/longest daily streak from completed WorkoutSessions and six
badges (first session, 10 and 50 sessions, 7- and 30-day streaks, a
100kg+ completed lift) from existing session/session-item data - no new
tables, since everything needed is already recorded.

Found and fixed a real Carbon 3 behavior change via testing: diffInDays()
no longer returns an absolute value by default (unlike Carbon 2) - it
returns a signed float. My longest-streak calculation used a strict
=== 1 check against the raw result, which silently always failed
because float(-1) or float(1) never strictly equals int 1. Fixed with
abs() plus an explicit (int) cast. Worth remembering for any other
diffIn*() usage in this codebase going forward.

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

app/Http/Controllers/DashboardController.php

@@ -3,6 +3,7 @@
 namespace App\Http\Controllers;
 
 use App\Models\WorkoutSession;
+use App\Support\Gamification;
 use Illuminate\Support\Facades\Auth;
 use Illuminate\View\View;
 
@@ -55,6 +56,9 @@ class DashboardController extends Controller
             ? round($weightLogs->last()->weight_kg - $weightLogs->first()->weight_kg, 2)
             : null;
 
+        // Streaks and badges
+        $gamification = Gamification::forUser($user);
+
         return view('dashboard', compact(
             'workoutsCount',
             'sessionsCount',
@@ -63,7 +67,8 @@ class DashboardController extends Controller
             'recentSessions',
             'dailyActivity',
             'weightLogs',
-            'weightChange'
+            'weightChange',
+            'gamification'
         ));
     }
 }