chore: add pytest to PR template test plan

Aligns the PR checklist with the three checks CI actually runs, and
prefixes each with `uv run` so contributors don't have to think about
which Python environment to use.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: aqua5230

.github/pull_request_template.md

@@ -2,8 +2,9 @@
 <!-- One or two sentences explaining what this PR does and why. -->
 
 ## Test plan
-- [ ] `ruff check .`
-- [ ] `mypy .`
+- [ ] `uv run ruff check .`
+- [ ] `uv run mypy .`
+- [ ] `uv run pytest tests/`
 - [ ] Manually verified in menu bar mode / TUI mode (if UI-related)
 
 ## Notes for reviewer