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/render/ATTRIBUTION.md

@@ -0,0 +1,46 @@
+# Popup renderer attribution
+
+`glossary.js`, `popup.js`, and `reader.css` in this directory contain or adapt
+GPL-licensed work from the projects below. Each file carries its own
+`SPDX-License-Identifier: GPL-3.0-or-later` header and the upstream copyright
+lines; the repository's root `LICENSE` has the full GNU GPL version 3 text.
+
+- **GameSentenceMiner PR #549** — the direct source of all three files.
+  `glossary.js` is extracted from `GSM_Overlay/features/hoshidicts/reader.js`
+  (structured-content renderer, furigana segmentation, pitch-accent ruby,
+  dictionary style scoping). `popup.js` is
+  `GSM_Overlay/features/hoshidicts/popup.js` with the Anki mining, custom
+  definition, and audio surfaces removed. `reader.css` is
+  `GSM_Overlay/features/hoshidicts/reader.css`. GameSentenceMiner is licensed
+  under GPL-3.0-or-later.
+
+- **[Hoshi Reader](https://github.com/Manhhao/Hoshi-Reader/tree/c31c9d0ce376ff83bf6a91d908bf9f8e0fb4947b/Features/Popup)**
+  — the popup structure (headword, glossary cards, tab strip, metadata capsule)
+  and the furigana segmentation algorithm (`segmentFurigana`,
+  `segmentizeFurigana`, `getFuriganaKanaSegments`). Licensed under
+  GPL-3.0-or-later.
+
+- **[Yomitan](https://github.com/yomidevs/yomitan)** and its predecessor
+  **[Yomichan](https://github.com/FooSoft/yomichan)** — the structured-content
+  schema that `appendStructuredValue` renders, the `gloss-*` class names and
+  image-container markup it emits, and the allowed-tag, allowed-style, and
+  `data-sc-*` attribute conventions. Both are licensed under GPL-3.0-or-later.
+
+- **[hoshidicts](https://github.com/Manhhao/hoshidicts)** — the engine whose
+  lookup JSON these files render, vendored as the `third_party/hoshidicts`
+  submodule. Licensed under GPL-3.0.
+
+- **[Yomitan GSM](https://github.com/bpwhelan/yomitan-gsm)** — the dark popup
+  palette adapted by `reader.css`. Licensed under GPL-3.0-or-later.
+
+- **[Microsoft Fluent System Icons](https://github.com/microsoft/fluentui-system-icons)**
+  — native action and status icons use the 20px Regular SVG subset in
+  `../icons/fluent/`. That directory includes the MIT license and a
+  `sources.json` manifest pinning the upstream revision and original paths.
+  `scripts/vendor-fluent-icons.py` generates the local `../icons.css` masks;
+  icons inherit theme colors and require no runtime external requests.
+
+Dictionary archives are not redistributed. Imported dictionaries keep whatever
+source, license, and attribution metadata their own index carries, and any CSS a
+dictionary ships is applied by `applyDictionaryStyles` scoped to that
+dictionary's own glossary content.