Stage 15 — PWA complete: install prompt + Web Push notifications

Dependency:
- minishlink/web-push v10 (VAPID JWT + aes128gcm payload encryption)
- Dockerfile: add curl, mbstring, gmp extensions (web-push needs ext-curl)

VAPID:
- config/webpush.php from env; `php artisan push:vapid` generates keypair
- Shared platform keypair; .env.example has empty placeholders

Schema:
- push_subscriptions (user/company, endpoint unique, p256dh, auth, encoding)

WebPushService:
- send / sendToUser / dispatch via WebPush::flush
- Auto-prunes subscriptions reported expired (404/410)

Subscribe flow:
- POST /push/subscribe + /push/unsubscribe (auth, tenant)
- Tenant panel JS subscribes after SW registration with VAPID public key

Service worker (/sw.js):
- Cache v2, push listener → showNotification, notificationclick → focus/open

Install prompt:
- Floating "Instalează aplicația" button wired to beforeinstallprompt

Staff push:
- WorkOrder master_id change → push to assigned mechanic
- Settings "Test notificare push" action

Tests (6 new):
- subscribe stores + upserts; requires auth (401); validation (422);
  service configured; sendToUser with no subs returns zero

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Models/Tenant/PushSubscription.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace App\Models\Tenant;
+
+use App\Models\Concerns\BelongsToTenant;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class PushSubscription extends Model
+{
+    use BelongsToTenant;
+
+    protected $fillable = [
+        'company_id', 'user_id', 'endpoint',
+        'public_key', 'auth_token', 'content_encoding', 'user_agent',
+    ];
+
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+}