Add dc_only parameter to all strategy endpoints. When true, filters
results to include only tickers present in the ETF table, supporting
DC pension investment constraints where only ETFs are allowed.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Pydantic v2's model_dump(mode="json") serializes Decimal as strings (e.g.,
"33.33" instead of 33.33), causing frontend crashes when calling .toFixed()
on string values. Introduced FloatDecimal type alias with PlainSerializer
to ensure Decimal fields are serialized as floats in JSON responses.
Also fixed frontend Transaction interface to match backend field names
(created_at → executed_at, transaction_type → tx_type).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
