Infer quote overlay state in notifications

[Pigbibi]

Summary

• infer quote-overlay state from known signal snapshot source names
• keep explicit quote_overlay_used values authoritative

Verification

• PYTHONPATH=.:../QuantPlatformKit/src ../QuantPlatformKit/.venv/bin/python -m py_compile notifications/renderers.py
• PYTHONPATH=.:../QuantPlatformKit/src ../QuantPlatformKit/.venv/bin/ruff check notifications/renderers.py
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Mark mixed fallback sources as no overlay

When any symbols use fallback pricing, application/execution_service.py records price_source_mode as mixed_market_quote_<fallback> and main.py copies that into signal_snapshot.latest_price_source; those values are already localized as mixed_market_quote_snapshot_close / mixed_market_quote_historical_close. Because this allowlist only matches the exact fallback source names, those normal fallback runs still render quote overlay unknown even though they are market-quote/fallback modes with no live quote overlay. Please include the mixed market-quote fallback modes in the false inference.

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