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/components/block_editor_components.ex

@@ -416,7 +416,8 @@ defmodule BerrypodWeb.BlockEditorComponents do
     filtered =
       assigns.allowed_blocks
       |> Enum.filter(fn {_type, def} ->
-        filter == "" or String.contains?(String.downcase(def.name), filter)
+        filter == "" or String.contains?(String.downcase(def.name), filter) or
+          String.contains?(String.downcase(Map.get(def, :description, "")), filter)
       end)
       |> Enum.sort_by(fn {_type, def} -> def.name end)
 
@@ -454,7 +455,10 @@ defmodule BerrypodWeb.BlockEditorComponents do
             class="block-picker-item"
           >
             <.icon name={def.icon} class="size-5" />
-            <span>{def.name}</span>
+            <span class="block-picker-item-name">{def.name}</span>
+            <span :if={def[:description]} class="block-picker-item-desc">
+              {def.description}
+            </span>
           </button>
 
           <p :if={@filtered_blocks == []} class="block-picker-empty">