fix(build): bundle kokoro source files for transformers runtime introspection

transformers opens .py source files at runtime to check attention/MoE
implementation via regex (e.g. _can_set_attn_implementation). PyInstaller's
--hidden-import only bundles .pyc bytecode, so kokoro/modules.py was missing
from the bundle causing a FileNotFoundError on Kokoro model load.

Switch from individual --hidden-import entries to --collect-all kokoro in both
build_binary.py and voicebox-server.spec. The kokoro package is 172K so no
meaningful bundle size impact.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

backend/build_binary.py

@@ -241,20 +241,13 @@ def build_server(cuda=False):
             "--collect-submodules",
             "tada",
             # Kokoro 82M — lightweight TTS engine using misaki G2P
+            # collect-all is required because transformers introspects .py source
+            # files at runtime (e.g. _can_set_attn_implementation opens the class
+            # file); hidden-import alone only bundles bytecode.
             "--hidden-import",
             "backend.backends.kokoro_backend",
-            "--hidden-import",
+            "--collect-all",
             "kokoro",
-            "--hidden-import",
-            "kokoro.pipeline",
-            "--hidden-import",
-            "kokoro.model",
-            "--hidden-import",
-            "kokoro.istftnet",
-            "--hidden-import",
-            "kokoro.modules",
-            "--hidden-import",
-            "kokoro.custom_stft",
             # misaki ships G2P data files (dictionaries, phoneme tables)
             # that must be bundled for espeak/en/ja/zh G2P to work
             "--collect-all",