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

.gitignore

@@ -20,6 +20,8 @@ coverage/
 /main-entry.js
 /main-entry.js.map
 
+/build/hachidori/
+
 # Logs
 *.log
 npm-debug.log*