[data-quality][domain] Normalize symbol metadata, asset class, and quote-convention assumptions

[dmidlo]

Parent: #93

Group: Domain and modeling readiness

Scope:

• Normalize symbols into asset classes such as FX, metals, oil, indexes, and unknown.
• Validate base/quote currency assumptions for FX pairs.
• Capture pip-size, quote-side, and bid-only M1 assumptions in quality metadata.
• Support symbol aliases where the repository already has or needs mapping rules.

Acceptance criteria:

• Quality reports include normalized symbol metadata when available.
• Unknown symbols are allowed but produce explicit metadata warnings.
• Tests cover EURUSD, JPY pairs, metals/index examples if supported, and unknown symbols.