feat(dictionary): add Hachidori backend support

- Add backend selection, setup gating, Anki integration, and external host support
- Add launcher flags, documentation, packaging, and focused tests
- Open on-demand overlay modals on the first attempt

src/config/definitions/template-sections.ts

@@ -1,6 +1,14 @@
 import { ConfigTemplateSection } from './shared';
 
 const CORE_TEMPLATE_SECTIONS: ConfigTemplateSection[] = [
+  {
+    title: 'Dictionary Backend',
+    description: ['Select the dictionary lookup backend: yomitan or hachidori.'],
+    notes: [
+      'Restart SubMiner after changing the backend. Each backend keeps separate settings and dictionaries.',
+    ],
+    key: 'dictionaryBackend',
+  },
   {
     title: 'Japanese Subtitle Generation',
     description: [