fix(logging): prevent duplicate OpenTAKServer log lines

[fallenmi]

Summary

• stop the shared OpenTAKServer logger from propagating records to the root logger
• add a behavioral regression test proving the named handler receives one record while the root handler receives none

Root cause

OpenTAKServer configures handlers directly on its named logger, but the logger retained Python's default propagate=True. When a dependency or runtime also configured the root logger, the same record was emitted by both handler chains.

The named logger's existing file and TTY handlers are unchanged. In non-TTY environments, this intentionally removes the accidental bare root/stderr copy while preserving the configured file output.

Validation

• regression test confirmed failing before the source change and passing after it
• .venv/bin/python -m pytest -q (1 passed, 1 skipped)
• .venv/bin/python -m black --check opentakserver/extensions.py tests/test_logging.py
• .venv/bin/python -m isort --check-only opentakserver/extensions.py tests/test_logging.py
• .venv/bin/python -m flake8 opentakserver/extensions.py tests/test_logging.py

Thanks to @TX-RX for the clear report and suggested direction.

Fixes #304

Generated-by: OpenAI Codex (GPT-5)