mavweb: add notifications history page at /notifications

RecentNudges IPC method, store adapter, dispatch, and client proxy.
Web UI at /notifications showing recent nudge history with color-coded
outcomes, nav links from /dash and /history.

cmd/mavweb/history.html

@@ -23,7 +23,7 @@
   .msg-err{background:#ffe6e6;display:block!important}
 </style>
 <h1>maven · command history</h1>
-<nav><a href=/dash>dash</a> <a href=/tools>tools</a> <a href=/auth/passkey>passkey</a></nav>
+<nav><a href=/dash>dash</a> <a href=/tools>tools</a> <a href=/auth/passkey>passkey</a> <a href=/notifications>notifications</a></nav>
 <p class=count>{{len .Facts}} facts shown (newest first)</p>
 <div id=msg></div>
 <table>