Add economic and specialized source references #69

Depends on #68 for the reference-table contract. Add standalone pages for fixed income and macroeconomic data. Preserve and update the fundamentals and alternative-data pages to use the same comparison dimensions. Create standalone research-factor and prediction-market pages when each verified inventory has at least three sources and distinct selection criteria.

Move duplicated factor and prediction-market material to its authoritative page and leave concise cross-links. Map wrapped sources to exact public provider classes and capabilities. Extend the private recommendation list with missing adapters ranked by demand, coverage gap, provider fit, access and licensing boundary, and testing burden.

Verification:

• uv run mkdocs build --strict
• uv run pytest tests/test_provider_registry_contract.py -q
• Fixed-income and macroeconomic pages appear in navigation.
• Factor and prediction-market categories satisfy the standalone threshold or remain linked sections with recorded evidence.
• Every retained source has current official evidence and a reproducible acquisition route.

Done means every specified asset class has one authoritative public reference location and the missing-adapter recommendations remain private.

Plan reference: ml4t-data-dev/.workspace/work/asset-class-source-reference/plan.md - Issue 2 in milestone 0.2.1 - Asset-class data-source reference.