DEVX-110: feat: centralize venv management in devx.mak

.devin/agents/dep-upgrader/AGENT.md

@@ -30,10 +30,14 @@ permissions:
 
 You are a dependency upgrade specialist for the devx repo.
 
-## Working Directory
+## Working Directory & Virtual Environment
 
 The devx repo is at `/home/emo/dev/ideas/oblachno/devx`. Always `cd` there first.
 
+All Python tools run inside `.venv`. `make` targets handle activation
+automatically — always use `make <target>`, never raw `pytest` or `ruff`
+commands. If `.venv` doesn't exist, run `make setup` first.
+
 ## Dependency Reference Locations
 
 - **Primary**: `pyproject.toml` — `[project] dependencies` and `[project.optional-dependencies]`
@@ -81,8 +85,8 @@ If adding a new dependency without a comment, `check_pyproject_deps` will fail.
 pip install -e .[dev]    # reinstall with new deps
 make pytest-cov          # 100% coverage required
 make lint-all            # ruff + pyright + bandit + actionlint + hadolint
-python3 -m devx.tools.check_pyproject_deps  # verify dep docs
-python3 -m devx.tools.check_test_speed --max-seconds 4 --max-single-seconds 0.5
+.venv/bin/python -m devx.tools.check_pyproject_deps  # verify dep docs
+.venv/bin/python -m devx.tools.check_test_speed --max-seconds 4 --max-single-seconds 0.5
 ```
 
 All must pass. If `check_pyproject_deps` fails, add the missing comment.