test(commands): add unit tests for command handlers

Add comprehensive unit tests for all command handlers:
- TestHelperFunctions: is_group, get_group_id, get_user_id, get_room_id
- TestCmdBounty: lists bounties, handles empty
- TestCmdMy: shows tracked in groups, personal in DM
- TestCmdAdd: add bounty success, validation
- TestCmdUpdate: update bounty, permission denied, invalid ID
- TestCmdDelete: delete bounty, invalid ID
- TestCmdTrack: track in group, reject in DM
- TestCmdUntrack: untrack in group, reject in DM
- TestCmdStart: group vs DM behavior
- TestCmdHelp: shows all commands

Also fix conftest.py to remove obsolete fresh_db fixture
that referenced non-existent db module.

All 55 tests pass.

Addresses han's feedback on PR #33

apps/telegram-bot/tests/conftest.py

@@ -6,22 +6,5 @@ from pathlib import Path
 
 import pytest
 
-# Add the app directory to path so `import db` works when running pytest
+# Add the app directory to path so imports work when running pytest
 sys.path.insert(0, str(Path(__file__).parent.parent))
-
-
-@pytest.fixture(autouse=True)
-def fresh_db(monkeypatch):
-    """Replace DB_PATH with a temp file before any test runs."""
-    import db as _db
-
-    tmp = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
-    tmp_path = Path(tmp.name)
-    tmp.close()
-
-    monkeypatch.setattr(_db, "DB_PATH", tmp_path)
-    _db.init_db()
-
-    yield tmp_path
-
-    tmp_path.unlink(missing_ok=True)