Add body weight logging with a trend on the dashboard

No way existed to log body weight over time - only the single
self-reported value from the signup profile - and the dashboard showed
session activity but nothing about physical progress, which is usually
the main reason people keep using a fitness app.

Adds a WeightLog model (one entry per user per day, re-logging the same
day updates it rather than duplicating), a quick-add form and trend
summary on the dashboard, and delete support.

Found and fixed a real bug along the way: the first implementation used
WeightLog::updateOrCreate() with a raw ['logged_at' => $date] match
array, which silently failed to find the same-day entry because the
`date` cast stores full datetime strings ('2026-01-01 00:00:00') while
the match array holds a plain 'Y-m-d' string - so re-logging the same
day hit a unique-constraint violation instead of updating. Fixed by
using a whereDate() lookup instead, which is comparison-format-safe.

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

app/Http/Controllers/DashboardController.php

@@ -49,13 +49,21 @@ class DashboardController extends Controller
             ->groupBy(function ($s) { return $s->created_at->format('Y-m-d'); })
             ->map->count();
 
+        // Body weight trend
+        $weightLogs = $user->weightLogs()->orderBy('logged_at')->get(['id', 'weight_kg', 'logged_at']);
+        $weightChange = $weightLogs->count() >= 2
+            ? round($weightLogs->last()->weight_kg - $weightLogs->first()->weight_kg, 2)
+            : null;
+
         return view('dashboard', compact(
             'workoutsCount',
             'sessionsCount',
             'completedSessions',
             'completionRate',
             'recentSessions',
-            'dailyActivity'
+            'dailyActivity',
+            'weightLogs',
+            'weightChange'
         ));
     }
 }

app/Http/Controllers/WeightLogController.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Models\WeightLog;
+use Illuminate\Http\RedirectResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+
+class WeightLogController extends Controller
+{
+    public function store(Request $request): RedirectResponse
+    {
+        $data = $request->validate([
+            'weight_kg' => ['required', 'numeric', 'min:20', 'max:400'],
+            'logged_at' => ['nullable', 'date', 'before_or_equal:today'],
+        ]);
+
+        $loggedAt = $data['logged_at'] ?? now()->toDateString();
+
+        // updateOrCreate's raw match array compares logged_at as a literal string,
+        // which doesn't reliably match how the `date` cast stores it - use a
+        // date-aware lookup instead.
+        $entry = WeightLog::where('user_id', Auth::id())->whereDate('logged_at', $loggedAt)->first()
+            ?? new WeightLog(['user_id' => Auth::id(), 'logged_at' => $loggedAt]);
+        $entry->weight_kg = $data['weight_kg'];
+        $entry->save();
+
+        return back()->with('status', __('app.weight_log.saved'));
+    }
+
+    public function destroy(WeightLog $weightLog): RedirectResponse
+    {
+        if ($weightLog->user_id !== Auth::id()) {
+            abort(403);
+        }
+
+        $weightLog->delete();
+
+        return back()->with('status', __('app.weight_log.deleted'));
+    }
+}