Define the canonical enriched market model and enrichment pipeline #253

Goal

Define the provider-neutral market model that becomes the canonical data foundation of TKSBrokerAPI 2.x.

Scope

• Model instruments, venues, sessions, prices, market data, accounts, portfolios, positions, orders, executions, currencies, and provider capabilities through common domain contracts.
• Define how raw provider data is normalized and enriched.
• Preserve provider-specific metadata as optional extensions without making it the core contract.
• Define stable identifiers and provenance for enriched values.
• Keep calculations and enrichment independent from presentation formats.

Acceptance criteria

• The canonical market model is documented and versionable.
• Raw provider data and enriched domain data have explicit boundaries.
• Enriched values retain source/provenance information where relevant.
• Provider-specific extensions do not change common consumer contracts.
• The model is suitable for T-Invest and future broker, exchange, and crypto connectors.