feat(notifications): wire publisher + async feature flag (GOO-173)

Phase 1 step 3 — make NotificationsPublisher available via DI and
introduce the NOTIFICATIONS_ASYNC_ENABLED flag that will gate the
listener cutover.

- NotificationsAsyncConfig: tiny injectable that reads
  NOTIFICATIONS_ASYNC_ENABLED (truthy: 1/true/yes/on, default disabled).
  Callers don't touch process.env directly; per-category rollout can be
  added later without churn in listeners.
- NotificationsModule providers/exports now include NotificationsPublisher
  and NotificationsAsyncConfig so listeners/handlers can inject them.
- Tests (14 specs on the flag + 4 on the publisher = 18 total green):
  * default disabled when unset
  * truthy parsing (1, true, TRUE, yes, on, padded)
  * falsy parsing (false, 0, no, off, empty, unknown)
  * describe() reports human-readable state

No call sites updated yet — next commit migrates the first listener
(PaymentCompletedListener pilot) onto the publisher with the flag check.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/globals.css

@@ -117,6 +117,18 @@
   [data-numeric] {
     font-variant-numeric: tabular-nums;
   }
+
+  /* Consistent focus-visible ring for all interactive elements */
+  :focus-visible {
+    outline: 2px solid hsl(var(--ring));
+    outline-offset: 2px;
+    border-radius: var(--radius);
+  }
+
+  /* Remove outline for mouse users; keep it for keyboard navigation */
+  :focus:not(:focus-visible) {
+    outline: none;
+  }
 }
 
 /* Mapbox popup theming */