feat(config): add VAPID settings for Web Push

Configure VAPID keys and claims to securely enable web push notifications.

config/settings/base.py

@@ -220,6 +220,14 @@ X_FRAME_OPTIONS = "DENY"
 BASE_URL = env("BASE_URL", default="http://localhost:8000")
 SITE_NAME = env("SITE_NAME", default="Project Management")
 
+# ── Web Push (VAPID) ────────────────────────────────────────────────────────────
+
+VAPID_PUBLIC_KEY = env("VAPID_PUBLIC_KEY", default="")
+VAPID_PRIVATE_KEY = env("VAPID_PRIVATE_KEY", default="")
+VAPID_CLAIMS = {
+    "sub": f"mailto:{env('DEFAULT_FROM_EMAIL', default='admin@example.com')}"
+}
+
 # ── API Docs ──────────────────────────────────────────────────────────────────
 
 SPECTACULAR_SETTINGS = {