fix(backend): bundle unidic-lite for misaki Japanese G2P (#514)

fugashi (pulled in by misaki[ja]) needs a MeCab dictionary at runtime.
The `unidic` package that ships today contains no data — it relies on
`python -m unidic download` (~526MB), which isn't run by `just setup`
and won't survive PyInstaller freezing.

Switch to `unidic-lite`, which bundles a MeCab-compatible dict inside
the wheel (~50MB). Collect its data files in build_binary.py so frozen
builds also pick up the dicdir. Same failure mode and same fix shape as
the existing en_core_web_sm pre-install.

backend/build_binary.py

@@ -287,6 +287,12 @@ def build_server(cuda=False):
             "en_core_web_sm",
             "--hidden-import",
             "en_core_web_sm",
+            # unidic-lite ships the MeCab dictionary used by fugashi (pulled in
+            # by misaki[ja]). The dict lives in unidic_lite/dicdir/ and is
+            # discovered via the package's DICDIR constant, so the data files
+            # must be collected or Japanese Kokoro voices crash at runtime.
+            "--collect-all",
+            "unidic_lite",
             "--hidden-import",
             "loguru",
         ]

backend/requirements.txt

@@ -46,6 +46,11 @@ misaki[en,ja,zh]>=0.9.4
 # spacy model for misaki English G2P — must be pre-installed or misaki
 # tries spacy.cli.download() at runtime which crashes frozen builds
 en_core_web_sm @ https://github.com/explosion/spacy-models/releases/download/en_core_web_sm-3.8.0/en_core_web_sm-3.8.0-py3-none-any.whl
+# fugashi (pulled in by misaki[ja]) needs a MeCab dictionary on disk.
+# unidic-lite ships one inside the wheel (~50MB); the full `unidic` package
+# requires `python -m unidic download` (~526MB) which breaks frozen builds
+# for the same reason en_core_web_sm does.
+unidic-lite>=1.0.8
 
 # Audio processing
 librosa>=0.10.0