add admin UX quick wins: nav guard, block descriptions, input labels

- rename "Providers" to "Print providers" in sidebar (#110)
- add LiveView navigation guard to EditorKeyboard hook — intercepts
  link clicks in capture phase when editor has unsaved changes (#103)
- add description field to all 26 block types, shown as subtitle in
  block picker; filter searches descriptions too (#104)
- add visible column headers (Label / Path) and proper sr-only labels
  with for attributes on nav editor inputs (#106)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/admin/components.css

@@ -1465,7 +1465,7 @@
 
   @media (min-width: 40em) {
     border-radius: 0.75rem;
-    max-width: 28rem;
+    max-width: 36rem;
   }
 }
 
@@ -1493,9 +1493,10 @@
 }
 
 .block-picker-item {
-  display: flex;
-  align-items: center;
-  gap: 0.5rem;
+  display: grid;
+  grid-template-columns: 1.25rem 1fr;
+  gap: 0.25rem 0.5rem;
+  align-items: start;
   padding: 0.625rem 0.75rem;
   border: 1px solid var(--t-border-default);
   border-radius: 0.375rem;
@@ -1513,6 +1514,18 @@
   }
 }
 
+.block-picker-item > .size-5 {
+  grid-row: 1 / -1;
+  margin-top: 0.0625rem;
+}
+
+.block-picker-item-desc {
+  grid-column: 2;
+  font-size: 0.6875rem;
+  line-height: 1.3;
+  color: color-mix(in oklch, var(--t-text-primary) 55%, transparent);
+}
+
 .block-picker-empty {
   grid-column: 1 / -1;
   text-align: center;
@@ -2280,6 +2293,20 @@
 
 /* Navigation editor */
 
+.nav-editor-labels {
+  display: flex;
+  gap: 0.5rem;
+  padding: 0 0.5rem;
+  font-size: 0.75rem;
+  font-weight: 500;
+  color: color-mix(in oklch, var(--t-text-primary) 55%, transparent);
+
+  & span {
+    flex: 1;
+    min-width: 0;
+  }
+}
+
 .nav-editor-item {
   display: flex;
   align-items: center;