add perf history and alerts

[jeffbrennan]

• sparkparse/history.py: append-only RunRecord store with Delta (primary)
  and JSONL (fallback) formats, record_from_dfs reuses analyze.find_* helpers
• sparkparse/alerts.py: AlertConfig model, TOML loader, check_alerts with
  threshold/pct_increase/absolute_increase conditions and log/raise/file
  dispatch
• sparkparse/capture.py: history_path, log_name, alert_config params wired
  into exit for get/analyze actions
• sparkparse/app.py: history and check-alerts CLI commands
• sparkparse/models.py: RunRecord Pydantic model
• sparkparse/storage.py: append_text helper
• pyproject.toml: optional [delta] extra