Split notification targets from strategy plugin consumers

[Pigbibi]

Summary

• split general market-regime notifications into notification_targets instead of a synthetic strategy consumer
• emit notification target artifacts with target_type=notification_target and no strategy field
• update runner docs, examples, and bilingual notification/log wording

Verification

• PYTHONPATH=src .venv/bin/pytest tests/test_strategy_plugin_runner.py -q
• PYTHONPATH=src .venv/bin/pytest -q
• PYTHONPATH=src .venv/bin/ruff check .
• git diff --check