feat(dictionaries): add hunspell dictionary module

modules/dictionaries.nix

@@ -0,0 +1,53 @@
+# Hunspell dictionaries, joined into one directory so anything needing a
+# dictionary *path* can be pointed at a single store path.
+#
+# Two consumers, two mechanisms:
+#   - LibreOffice needs nothing beyond the package being installed: its wrapper
+#     scans `share/hunspell` in every NIX_PROFILES entry.
+#   - Gecko apps (LibreWolf, Thunderbird) need `spellchecker.dictionary_path`
+#     set explicitly — there is no /usr/share/hunspell on NixOS and wrapFirefox
+#     wires up nothing itself. Point that pref at `local.dictionaries.path`.
+#
+# Chromium-based browsers are NOT served by this: they ignore hunspell and
+# fetch their own dictionaries, selected by enterprise policy.
+#
+# Which languages is a personal choice, so the default is empty; a consumer sets
+# `local.dictionaries.packages = [ pkgs.hunspellDicts.de_DE ];`. en-US ships
+# inside Firefox/Thunderbird already and does not need listing for those.
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.local.dictionaries;
+
+  joined = pkgs.symlinkJoin {
+    name = "hunspell-dicts";
+    paths = cfg.packages;
+  };
+in
+{
+  options.local.dictionaries = {
+    packages = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ ];
+      example = lib.literalExpression "[ pkgs.hunspellDicts.de_DE ]";
+      description = ''
+        Hunspell dictionary packages to install and expose via
+        `local.dictionaries.path`.
+      '';
+    };
+
+    path = lib.mkOption {
+      type = lib.types.str;
+      readOnly = true;
+      description = ''
+        Directory holding every `packages` dictionary. Feed this to
+        `spellchecker.dictionary_path` in Gecko apps.
+      '';
+    };
+  };
+
+  config = {
+    local.dictionaries.path = "${joined}/share/hunspell";
+    home.packages = lib.optional (cfg.packages != [ ]) joined;
+  };
+}