#16324 feat(web): rework the cost-overrides panel and modal

Description

Reworks the Cost Overrides panel on the admin Language Models page.

• Modal: adding and editing happen in a "New / Edit Cost Override" modal instead of an inline form. It runs on Formik with a Yup schema, like the language-model provider modals: Save / Add stay disabled until the form is valid and changed, and Enter submits.
• Fields: InputHorizontal rows with short titles and descriptions. The three rates use InputCurrency (2 decimals). The edit path shows the override's model in the model selector, disabled.
• Cards: each override is a SelectCard like the provider cards: model icon, model name, provider and update date, the rates on a line below, and trash / settings buttons beside the title. Delete now asks for confirmation.
• Search focus: InputSingleSelect and SimpleModelSelector take a container, passed to the Dropdown. The modal passes its content element so the model search field keeps focus inside the dialog's focus trap.
• Copy updated in all nine locales; unused placeholder keys removed.

UI only: it works with the current cost-override API. The data-model change (overrides referencing model_configuration) comes in a separate PR.

Changes

No overrides

>1 overrides

Creating new override

Editing existing override

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Summary by cubic

Reworks the Cost Overrides panel on the admin Language Models page: adding and editing now happen in a New/Edit Cost Override modal, and each override renders as a card matching the provider cards above it. UI only — the overrides API is unchanged.

New Features

• Add/edit moved from an inline form to a Formik + Yup modal; Add/Save stays disabled until the form is valid and changed, and Enter submits. Fields use InputHorizontal with short titles and unit descriptions.
• Rates use InputCurrency with unlimited precision, so sub-cent negotiated rates ($0.075, $0.01875) save and display exactly; each card lists In, Out, and (when set) Cache as separate items on a line under the description. The edit path shows the override's model in a disabled selector, or a read-only field when no configured model matches.
• Delete now asks for confirmation, disables itself while the request runs, and shows success/error toasts; copy is updated in all nine locales, unused placeholder keys were removed, and the API error path now reuses parseErrorDetail.
• Tests that drove a mocked model picker were dropped: they didn't exercise the real modal.

Bug Fixes

• InputSingleSelect and SimpleModelSelector accept a container passed to the Dropdown, so the model search field keeps focus inside the modal's focus trap.

Summary by CodeRabbit

• New Features

  • Added modal-based forms for creating and editing cost overrides with validation and model selection.
  • Cost rates now support unlimited precision and display separate input, output, and cache values alongside provider and update time.
  • Added edit and confirmation-based delete actions with success and error notifications.
  • Improved dropdown placement within dialogs and constrained layouts.

• Localization

  • Updated cost-override labels, descriptions, units, titles, rate details, and confirmation messages across supported languages.