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/scripts/firefox-package.json

@@ -0,0 +1,21 @@
+{
+  "excludedFiles": [
+    "avif-sequence.js",
+    "capture-audio-worklet.js",
+    "capture-buffer.js",
+    "capture-content.js",
+    "capture-encoder-client.js",
+    "capture-encoder-worker.js",
+    "capture-frame-client.js",
+    "capture-frame-worker.js",
+    "capture-host.js",
+    "capture-session.js",
+    "capture-speech.js",
+    "capture-timeline.js",
+    "capture.css",
+    "capture.html",
+    "capture.js",
+    "vendor/avif-encoder.mjs",
+    "vendor/avif-encoder.wasm"
+  ]
+}