feat(tg-fitness-bot): add test suite with pre-commit hook

pytest + pytest-asyncio in flake.nix. 53 tests covering parser
(all formats, error cases) and db (CRUD, soft delete, update,
stats, pagination). Pre-commit hook runs tests when fitness bot
files are staged.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,18 @@
+import sys
+from pathlib import Path
+
+import pytest
+
+# Add project root to path so tests can import modules directly
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+
+@pytest.fixture
+def tmp_db(monkeypatch, tmp_path):
+    """Provide a fresh SQLite database for each test."""
+    import db
+
+    db_file = tmp_path / "test_workouts.db"
+    monkeypatch.setattr(db, "DB_PATH", db_file)
+    db.init_db()
+    return db_file