Add the credits by model panel to the DAP Impact Spend view

What does this MR do and why?

Adds the "Credits by model, by capability" panel to the DAP Impact Spend view: credits split by model and capability as a stacked bar list on the DuoWorkflows aggregation engine, top capabilities as segments and the rest rolled into Other.

Draft: blocked on, in order —

1. glql!511 (merged) (model dimension) plus a glql release and the gem/npm version bumps here
2. !255840 (merged) (stacked bar list with Load more)

Model logos, provider annotations and badges are a separate layer: !255850 (closed)

Known follow-up: production model_used is not populated yet (rollout in https://gitlab.com/gitlab-org/gitlab/-/issues/607369), so this panel shows a single unattributed row on real data until ingestion lands.

References

https://gitlab.com/groups/gitlab-org/-/work_items/23470

Screenshots or screen recordings

How to set up and validate locally

Enable the dap_impact_v1 feature flag, seed duo_workflows_workflows_enriched with credits data, then open /explore/analytics_dashboards/dap_impact?view=3.