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

docs/workflow/verification.md

@@ -63,6 +63,7 @@ bun run docs:build
   Content checks and informational size reporting run inside electron-builder hooks. See the
   [release guide](../RELEASING.md#package-contents-and-size-checks) for size reports
   and the installed-app verification checklist.
+- Dictionary backend windows: after a full build, run `xvfb-run -a bun run test:dictionary:electron` on headless Linux. It uses temporary profiles to check both named settings commands, backend session isolation, the overlay's external-link bridge, and Hachidori's native dictionary parser.
 - Coverage for the maintained source lane: `bun run test:coverage:src`
 - Deep/local full gate: default handoff gate above