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/cli/help.ts

@@ -25,6 +25,7 @@ ${B}Overlay${R}
   --show-visible-overlay         Show subtitle overlay
   --hide-visible-overlay         Hide subtitle overlay
   --yomitan                      Open Yomitan settings window
+  --hachidori                    Open Hachidori settings window
   --settings                     Open SubMiner settings window
   --setup                        Open first-run setup window
   --auto-start-overlay           Auto-hide mpv subs, show overlay on connect