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/options-core.ts

@@ -81,6 +81,13 @@ export function buildCoreConfigOptionRegistry(
   ] as const;
 
   return [
+    {
+      path: 'dictionaryBackend',
+      kind: 'enum',
+      enumValues: ['yomitan', 'hachidori'],
+      defaultValue: defaultConfig.dictionaryBackend,
+      description: 'Dictionary lookup backend. Restart SubMiner after changing this setting.',
+    },
     {
       path: 'logging.level',
       kind: 'enum',