chore: move model storage into project models/ directory

Models now live in <project>/models/ instead of ~/.8cut_models/ so
everything stays self-contained. Updated .gitignore to exclude
models/, .venv/, *.joblib, and *.pt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -3,5 +3,7 @@ __pycache__/
 *.pyo
 .pytest_cache/
 .worktrees/
-client/node_modules/
-client/src-tauri/target/
+.venv/
+models/
+*.joblib
+*.pt