Credits and usage visibility for Hex Agents

Introduced a credit model for Hex Agents, including monthly credit grants per user seat (Professional, Team, Enterprise, Explorer) and pooled add-on credits with auto top-ups. Implemented an effort-based consumption system that dynamically selects LLM models based on task complexity, context, and resource requirements, aiming for cost efficiency. Enhanced visibility by allowing users to view credit balances and per-prompt costs, and providing admins with historical usage logs, spend limit settings, and credit usage data within the Context Studio. This enables better budgeting, ROI calculation, and informed decisions on context curation and model selection.