feat: enforce 85% test coverage in CI and fix cross-platform strftime bug

Add pyproject.toml with pytest-cov config so CI fails if coverage drops
below 85%. Fix series_view _format_start using Linux-only %-I/%-d codes
that crash on Windows — use manual formatting instead.

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

.gitignore

@@ -6,5 +6,6 @@ nhl_standings.db
 **/__pycache__
 .venv/
 .coverage
+htmlcov/
 .pytest_cache/
 .claude/