[Backlog] Add Agent Bricks pricing workloads

[CheeYuTan]

Summary

Add first-class Lakemeter estimation for Databricks Agent Bricks, including Knowledge Assistant and Supervisor Agent workloads.

Billing data distinguishes AGENT_BRICKS and SUPERVISOR_AGENT billing origins, but Lakemeter does not currently expose an Agent Bricks workload or calculation model.

Scope

• Verify current public pricing, shared SKUs, billing units, free allowances, and additive underlying services from official Databricks sources.
• Model Knowledge Assistant and Supervisor Agent separately when their billable dimensions differ.
• Identify costs that must be estimated separately, such as Model Serving, Foundation Model API, AI Search, evaluation, or storage.
• Use practical planning inputs that can be reconciled with system.billing.usage metadata.
• Avoid inventing rates when only a billing origin, rather than a standalone SKU, is published.

Acceptance criteria

• Add appropriate Agent Bricks workload type or types, calculation APIs, and frontend forms.
• Resolve exact cloud, region, tier, workload mode, and SKU pricing without cross-region fallback.
• Persist all new fields in workload_config; no database schema migration.
• Show transparent monthly usage → DBUs → SKU rate → cost formulas.
• Include AI-assisted estimate creation, cloning, and Excel export.
• Explain additive and excluded underlying service costs in the UI.
• Add calculation, validation, persistence, parity, and export tests.
• Validate assumptions against official documentation and billing system-table fields before release.

[CheeYuTan]

Closing because Agent Bricks is expected to be deprecated, so Lakemeter will not add this workload.

[CheeYuTan]

The current Databricks pricing catalog still lists Agent Bricks as a product: https://www.databricks.com/product/pricing/agent-bricks. Reopening this as a backlog item; implementation should first confirm the current billable dimensions and whether a reliable estimator can be built without inventing rates.