fix(01-05): put src/ on sys.path so the Space can import the package

Second deploy (6eeb816) built cleanly and then died at startup with
`ModuleNotFoundError: No module named 'japanese_avatar'`. A Space installs
requirements.txt and nothing else - this repository is never pip-installed there -
so the src/ layout package was invisible to `python app.py`. Locally the dev venv
has it installed as editable, which is why every test passed.

Bootstrapped in app.py rather than through a PYTHONPATH Space variable: an env var
would make a clean checkout silently unrunnable and would not travel with the repo.

app.py

@@ -13,10 +13,22 @@ Python - which is what ``test_no_remount`` measures the avatar against.
 
 import html
 import os
+import sys
+from pathlib import Path
 
 import gradio as gr
 
-from japanese_avatar.ui.avatar_component import StatusLine, VrmStage
+# The Space runs `python app.py` with only requirements.txt installed - it never
+# pip-installs this repository - so the src/ layout package is not on sys.path there and
+# the import below raised ModuleNotFoundError on the first deploy (RUNTIME_ERROR on
+# 6eeb816). Locally the dev venv has the project installed and this is a no-op. Doing it
+# here rather than through a PYTHONPATH Space variable keeps the app runnable from a
+# clean checkout with no platform configuration to lose.
+_SRC = Path(__file__).resolve().parent / "src"
+if str(_SRC) not in sys.path:
+    sys.path.insert(0, str(_SRC))
+
+from japanese_avatar.ui.avatar_component import StatusLine, VrmStage  # noqa: E402
 
 # Serves avatar/ straight off disk, bypassing the Gradio cache, which is how the
 # browser reaches avatar.js, stage.html and tutor.vrm. Deliberately one dedicated