fix: use dedicated volume24h field in gemini-titan normalizer

[realfishsam]

Fixes #444

[realfishsam]

PR Review: VERIFIED

What This Does

Fixes the Gemini Titan event normalizer to read volume24h from the correct field on the raw API response. Previously, it read raw.volume (which is lifetime volume), causing UnifiedEvent.volume24h to report total volume instead of 24-hour volume. Also adds volume24h?: string to the GeminiRawEvent type definition.

Blast Radius

• core/src/exchanges/gemini-titan/normalizer.ts -- normalizeEvent method
• core/src/exchanges/gemini-titan/types.ts -- raw type definition

Findings

No blocking findings. The fix is correct:

• raw.volume24h is the right field for 24-hour volume
• raw.volume remains available on the type for lifetime volume (existing field, not removed)
• The parseFloat(...) : 0 fallback handles missing values cleanly
• Type definition correctly adds volume24h?: string as optional

PMXT Pipeline Check

• Field propagation: N/A (raw type only, not a unified type change)
• OpenAPI sync: N/A
• Type safety: OK

Semver Impact

patch -- bug fix for incorrect field mapping.

Risk

None. The change is narrowly scoped to Gemini Titan event normalization.