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/extension/media-limits.js

@@ -0,0 +1,10 @@
+// Shared media payload limits. Firefox keeps these validators without shipping
+// the Chrome-only recording and encoding implementation.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+export const MAX_LIVE_FRAME_BYTES = 64 * 1024 * 1024;
+export const MAX_PINNED_FRAME_BYTES = 32 * 1024 * 1024;
+export const MAX_FRAME_BYTES = 256 * 1024;
+export const MAX_WAV_BYTES = 1024 * 1024;
+export const CAPTURE_SAMPLE_RATE = 48_000;
+export const MAX_ANIMATED_AVIF_BYTES = 4 * 1024 * 1024;