ci: require icon_names input and drop ALL default

デフォルトの ["ALL"] を廃止し、空入力は明示的なエラーメッセージで
早期に失敗するようにする。

Author: claude

.github/workflows/build-icon.yml

@@ -6,7 +6,6 @@ on:
       icon_names:
         description: 'Figma component names (snake_case) as a JSON array, or ["ALL"] for all icons. e.g. ["align_left","album_fill"]'
         required: true
-        default: '["ALL"]'
 
 permissions:
   contents: write
@@ -32,11 +31,17 @@ jobs:
           node <<'EOF'
           const fs = require('node:fs');
 
+          const raw = (process.env.ICON_NAMES ?? '').trim();
+          if (raw === '') {
+            console.error('`icon_names` is required. Provide a JSON array of Figma component names, e.g. ["align_left","album_fill"], or ["ALL"] for all icons.');
+            process.exit(1);
+          }
+
           let iconNames;
           try {
-            iconNames = JSON.parse(process.env.ICON_NAMES);
+            iconNames = JSON.parse(raw);
           } catch {
-            console.error('`icon_names` must be a valid JSON array, e.g. ["IconArrowLeft"] or ["ALL"].');
+            console.error('`icon_names` must be a valid JSON array, e.g. ["align_left"] or ["ALL"].');
             process.exit(1);
           }