fix(nix): set VIRTUAL_ENV for ty to find site-packages

ty needs VIRTUAL_ENV to locate the Python environment's site-packages.
Without this, ty looks for .venv which doesn't exist in the Nix environment.

Also update justfile to conditionally use 'uv run' prefix only when
not in a Nix environment (detected via VIRTUAL_ENV). This makes
commands work for both Nix and non-Nix users.

Author: ryoppippi

flake.nix

@@ -144,6 +144,8 @@
                 UV_NO_SYNC = "1";
                 UV_PYTHON = "${python}/bin/python";
                 UV_PYTHON_DOWNLOADS = "never";
+                # Set VIRTUAL_ENV for tools like ty that look for site-packages
+                VIRTUAL_ENV = "${virtualenv}";
               };
 
               shellHook = ''

justfile

@@ -1,3 +1,6 @@
+# Helper to run Python commands (uses uv run if not in Nix environment)
+_run := if env("VIRTUAL_ENV", "") != "" { "" } else { "uv run " }
+
 # Install dependencies and pre-commit hooks
 install *extras:
 	uv sync {{ extras }}
@@ -15,31 +18,31 @@ lint-fix: format
 
 # Run all tests
 test:
-	uv run pytest
+	{{ _run }}pytest
 
 # Run tests with coverage
 coverage:
-	uv run pytest --cov --cov-report=term --cov-report=json --cov-report=html
+	{{ _run }}pytest --cov --cov-report=term --cov-report=json --cov-report=html
 
 # Run tool-specific tests
 test-tools:
-	uv run pytest tests
+	{{ _run }}pytest tests
 
 # Run example tests
 test-examples:
-	uv run pytest examples
+	{{ _run }}pytest examples
 
 # Run type checking
 ty:
-	uv run ty check stackone_ai
+	{{ _run }}ty check stackone_ai
 
 # Run gitleaks secret detection
 gitleaks:
 	gitleaks detect --source . --config .gitleaks.toml
 
 # Update version in __init__.py
 update-version:
-	uv run python scripts/update_version.py
+	{{ _run }}python scripts/update_version.py
 
 # Build package
 build: