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/core/services/startup-bootstrap.test.ts

@@ -15,6 +15,7 @@ function makeArgs(overrides: Partial<CliArgs> = {}): CliArgs {
     toggleVisibleOverlay: false,
     togglePrimarySubtitleBar: false,
     yomitan: false,
+    hachidori: false,
     settings: false,
     syncWindow: false,
     setup: false,