Bigger unread badge with a real count, and a Clear all action for notifications

The header bell's unread indicator was an 8px dot -- now a proper count
badge (capped at "9+"), matching the size/legibility of similar badges
elsewhere in the app. Notifications also gains "Clear all" next to
"Mark all read" -- a hard delete of the list (the same clear-all gesture
a phone's own notification centre uses), not another read-state flip.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

static/css/app.css

@@ -3944,6 +3944,9 @@
   .h-\[7px\] {
     height: 7px;
   }
+  .h-\[19px\] {
+    height: 19px;
+  }
   .h-\[22px\] {
     height: 22px;
   }
@@ -4169,6 +4172,9 @@
   .min-w-40 {
     min-width: calc(var(--spacing) * 40);
   }
+  .min-w-\[19px\] {
+    min-width: 19px;
+  }
   .min-w-\[220px\] {
     min-width: 220px;
   }