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/dictionary-group-state.js

@@ -0,0 +1,55 @@
+/*
+ * Shared dictionary-group state rules for extension consumers.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+(function () {
+  "use strict";
+
+  function normaliseGroupName(value) {
+    return (typeof value === "string" ? value : "")
+      .normalize("NFKC")
+      .trim()
+      .replace(/\s+/gu, " ");
+  }
+
+  function groupNameKey(value) {
+    return normaliseGroupName(value).toLowerCase();
+  }
+
+  function retainedMemberIds(value, installedIds) {
+    const seen = new Set();
+    return Array.isArray(value)
+      ? value.filter((id) => {
+        if (!installedIds.has(id) || seen.has(id)) return false;
+        seen.add(id);
+        return true;
+      })
+      : [];
+  }
+
+  function normaliseDictionaryGroups(value, installedDictionaries) {
+    if (!Array.isArray(value)) return [];
+    const installedIds = new Set(installedDictionaries.map((dictionary) => dictionary.id));
+    return value.map((group) => {
+      const id = typeof group?.id === "string" ? group.id : "";
+      const name = normaliseGroupName(group?.name);
+      if (id === "" || name === "") return null;
+      return { id, name, dictionaryIds: retainedMemberIds(group.dictionaryIds, installedIds) };
+    }).filter((group) => group !== null);
+  }
+
+  function pruneGroupMemberships(value, dictionaries) {
+    if (!Array.isArray(value)) return [];
+    const installedIds = new Set(dictionaries.map((dictionary) => dictionary.id));
+    return value.map((group) => ({
+      ...group,
+      dictionaryIds: retainedMemberIds(group.dictionaryIds, installedIds),
+    }));
+  }
+
+  globalThis.HDDictionaryGroups = {
+    normaliseGroupName, groupNameKey, normaliseDictionaryGroups, pruneGroupMemberships,
+  };
+}());