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/prepare-firefox.mjs

@@ -0,0 +1,48 @@
+#!/usr/bin/env node
+// Assemble the reviewed Firefox manifest with the shared extension sources.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+import { cp, mkdir, readFile, rm, writeFile } from "node:fs/promises";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath, pathToFileURL } from "node:url";
+
+const ROOT = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const SOURCE = resolve(ROOT, "extension");
+export const DEFAULT_FIREFOX_EXTENSION = resolve(ROOT, "test/tmp/firefox-extension");
+// Chrome-only capture and speech-recording files; scripts/package-store.py
+// reads the same list so the release XPI and the test build agree.
+export const FIREFOX_EXCLUDED_FILES = Object.freeze(
+  JSON.parse(await readFile(resolve(ROOT, "scripts/firefox-package.json"), "utf8")).excludedFiles,
+);
+
+function outputArgument(arguments_) {
+  if (arguments_.length === 0) return DEFAULT_FIREFOX_EXTENSION;
+  if (arguments_.length !== 2 || arguments_[0] !== "--output-dir" || arguments_[1] === "") {
+    throw new Error("usage: node scripts/prepare-firefox.mjs [--output-dir <path>]");
+  }
+  return resolve(arguments_[1]);
+}
+
+export async function prepareFirefoxExtension(output = DEFAULT_FIREFOX_EXTENSION) {
+  if (output === SOURCE || SOURCE.startsWith(`${output}/`)) {
+    throw new Error("The Firefox output directory must not contain extension/.");
+  }
+  await rm(output, { recursive: true, force: true });
+  await mkdir(output, { recursive: true });
+  await cp(SOURCE, output, { recursive: true });
+  const firefoxManifest = await readFile(resolve(SOURCE, "manifest.firefox.json"), "utf8");
+  await writeFile(resolve(output, "manifest.json"), firefoxManifest);
+  await rm(resolve(output, "manifest.firefox.json"));
+  await Promise.all(FIREFOX_EXCLUDED_FILES.map(path => rm(resolve(output, path))));
+  return output;
+}
+
+if (process.argv[1] && import.meta.url === pathToFileURL(resolve(process.argv[1])).href) {
+  try {
+    const output = await prepareFirefoxExtension(outputArgument(process.argv.slice(2)));
+    console.log(output);
+  } catch (error) {
+    console.error(error instanceof Error ? error.message : String(error));
+    process.exitCode = 1;
+  }
+}