feat: reward marker emission

[sqhell]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces a Featured App Rewards system that emits activity markers on the Canton ledger following billable tool calls. Key additions include the featured_app_rewards.py module for managing reward contracts, integration of marker emission into the server's billing flow, and a log filter to reduce noise from health check probes. Additionally, logging for authorization validation and semantic search has been enhanced. Review feedback identifies critical bugs in the new rewards module where snake_case keys are used instead of the camelCase keys required by the Canton JSON API v2, and notes an inconsistency in the default similarity threshold value.