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

vendor/hachidori/third_party/hoshidicts/include/module.modulemap

@@ -0,0 +1,5 @@
+module CHoshiDicts {
+    header "hoshidicts.h"
+    requires cplusplus
+    export *
+}