fix(master): review fixes for the Ledger UI (#18)

- icons/gen writes to the current directory so `go generate
  ./internal/master/web/icons` works (output verified byte-identical)
- share the registry-host check as imageref.IsRegistryHost (with test)
- agents fragment refreshes the "N machines" header count out of band
- ignore the saved machine filter at <=760px where the machine list is hidden
- aria-current on the active machine filter link, aria-pressed on theme toggle
- CLAUDE.md: icons package, SSE ping event, swarm_cluster_id

Claude-Session: https://claude.ai/code/session_01GAZsp3P7Qto6JnhipxWUJQ

internal/master/web/static/app.js

@@ -24,8 +24,10 @@
     themeButton.addEventListener('click', function () {
       var light = !root.classList.contains('t-light');
       root.classList.toggle('t-light', light);
+      themeButton.setAttribute('aria-pressed', String(light));
       save('localStorage', 'pu-theme', light ? 'light' : 'dark');
     });
+    themeButton.setAttribute('aria-pressed', String(root.classList.contains('t-light')));
   }
   if (colorScheme && colorScheme.addEventListener) {
     colorScheme.addEventListener('change', function (e) {
@@ -50,16 +52,21 @@
   var search = document.getElementById('q');
   if (search) search.value = filter.q;
 
+  // The machine list is hidden on narrow screens; a filter that cannot be
+  // seen or cleared there is ignored. Search still applies.
+  var narrow = window.matchMedia ? window.matchMedia('(max-width:760px)') : null;
+
   function applyFilter() {
     var box = document.getElementById('services');
     if (!box) return;
     var groups = box.querySelectorAll('.grp');
     var known = Array.prototype.some.call(groups, function (g) { return g.dataset.key === filter.machine; });
     if (filter.machine && !known) filter.machine = '';
+    var machine = narrow && narrow.matches ? '' : filter.machine;
     var q = filter.q.trim().toLowerCase();
     var any = false;
     Array.prototype.forEach.call(groups, function (g) {
-      var inMachine = !filter.machine || g.dataset.key === filter.machine;
+      var inMachine = !machine || g.dataset.key === machine;
       var shown = 0;
       Array.prototype.forEach.call(g.querySelectorAll('.row'), function (row) {
         var match = inMachine && (!q || (row.dataset.search || '').indexOf(q) !== -1);
@@ -71,8 +78,13 @@
     });
     var none = document.getElementById('nomatch');
     if (none) none.hidden = any || groups.length === 0;
-    each('#machines a', function (a) { a.classList.toggle('cur', a.dataset.machine === filter.machine); });
+    each('#machines a', function (a) {
+      var cur = a.dataset.machine === filter.machine;
+      a.classList.toggle('cur', cur);
+      if (cur) a.setAttribute('aria-current', 'true'); else a.removeAttribute('aria-current');
+    });
   }
+  if (narrow && narrow.addEventListener) narrow.addEventListener('change', function () { applyFilter(); });
   function saveFilter() { save('sessionStorage', 'pu-filter', JSON.stringify(filter)); }
 
   if (search) {