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>

lib/berrypod_web/live/admin/navigation.ex

@@ -158,13 +158,19 @@ defmodule BerrypodWeb.Admin.Navigation do
       </h3>
 
       <div class="space-y-2">
+        <div :if={@items != []} class="nav-editor-labels" aria-hidden="true">
+          <span>Label</span>
+          <span>Path</span>
+        </div>
         <div
           :for={{item, idx} <- Enum.with_index(@items)}
           class="nav-editor-item"
         >
           <div class="nav-editor-fields">
+            <label class="sr-only" for={"nav-#{@section}-#{idx}-label"}>Label</label>
             <input
               type="text"
+              id={"nav-#{@section}-#{idx}-label"}
               value={item["label"]}
               placeholder="Label"
               phx-blur="update_item"
@@ -173,8 +179,10 @@ defmodule BerrypodWeb.Admin.Navigation do
               phx-value-field="label"
               class="admin-input nav-editor-input"
             />
+            <label class="sr-only" for={"nav-#{@section}-#{idx}-href"}>Path</label>
             <input
               type="text"
+              id={"nav-#{@section}-#{idx}-href"}
               value={item["href"]}
               placeholder="/path"
               phx-blur="update_item"