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/anki-resources.js

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+import { buildAnkiFields } from "./anki-values.js";
+import { createAnkiDefinitionRenderer } from "./anki-glossary.js";
+import { ankiDigest } from "./anki-digest.js";
+
+const IMAGE_EXTENSIONS = new Set(["png", "jpg", "jpeg", "gif", "webp", "svg", "avif", "bmp", "ico", "tiff"]);
+
+export async function ankiMediaFilename(bytes, extension) {
+  return `hachidori_${await ankiDigest(bytes)}.${extension}`;
+}
+
+// Planning reads no dictionary bytes and uploads nothing. Stable generation
+// paths, unlike an engine's restart counter, keep first-field image identities
+// identical between preflight and the authoritative write.
+export async function buildAnkiResourceFields(request, templates, { document, dictionaryPaths, styles, audio = "" }) {
+  const media = new Map();
+  const source = { ...request, dictionaryMedia: [], dictionaryStyles: [] };
+  let plainRenderer, richRenderer;
+  function filenameFor(dictionary, path) {
+    const generationPath = Object.hasOwn(dictionaryPaths, dictionary) ? dictionaryPaths[dictionary] : null;
+    if (!generationPath) throw new Error(`The dictionary generation is no longer available: ${dictionary}`);
+    const key = JSON.stringify([dictionary, path]);
+    if (!media.has(key)) {
+      const suffix = path.split(".").at(-1).toLowerCase();
+      const bytes = new TextEncoder().encode(JSON.stringify([generationPath, path]));
+      media.set(key, ankiMediaFilename(bytes, IMAGE_EXTENSIONS.has(suffix) ? suffix : "bin")
+        .then(filename => ({ dictionary, path, filename })));
+    }
+    return media.get(key).then(item => item.filename);
+  }
+  const fields = await buildAnkiFields(request, templates, { audio, definition: async options => {
+    if (options.plain) {
+      plainRenderer ??= createAnkiDefinitionRenderer(document, source);
+      return plainRenderer(options);
+    }
+    richRenderer ??= Promise.resolve(styles()).then(dictionaryStyles =>
+      createAnkiDefinitionRenderer(document, { ...source, dictionaryStyles }, filenameFor));
+    return (await richRenderer)(options);
+  } });
+  return { fields, media: await Promise.all(media.values()) };
+}