fix: clarify AI model price configuration (#28372)

## Description

Model prices displayed in the Agents model form are read-only because
they are managed by AI Gateway. Add guidance and a link to the model
price configuration documentation, and rename the related documentation
subsection to **Configure model prices**.

> [!NOTE]
> Generated with Coder Agents by @ssncferreira.

docs/ai-coder/ai-gateway/cost-controls.md

@@ -213,7 +213,7 @@ https://github.com/coder/coder/blob/release/<VERSION>/coderd/aibridge/prices/dat
 Replace `<VERSION>` with a Coder minor version, for example `2.36`.
 
 To use your own price for any of these models, see
-[Set model prices](#set-model-prices).
+[Configure model prices](#configure-model-prices).
 
 > [!IMPORTANT]
 > Spend is an approximation. It can differ from what the provider bills, and
@@ -234,7 +234,7 @@ value means spend is under-counted. Because the price book ships with the
 release, a newly launched model is unpriced until you upgrade Coder or set a
 price for it yourself.
 
-### Set model prices
+### Configure model prices
 
 Use the experimental `coder exp ai-model-prices` command to set model prices
 for your deployment. It requires AI Governance, which is included with a

site/src/pages/AISettingsPage/ModelsPage/components/ModelForm.stories.tsx

@@ -466,6 +466,19 @@ export const CostEstimateFieldsAreImmutable: Story = {
 		await userEvent.click(
 			canvas.getByRole("button", { name: /cost estimate/i }),
 		);
+		await expect(
+			canvas.getByText(/model prices are managed by AI Gateway/i),
+		).toBeVisible();
+		await expect(
+			canvas.getByRole("link", {
+				name: /learn how to configure model prices/i,
+			}),
+		).toHaveAttribute(
+			"href",
+			expect.stringContaining(
+				"/ai-coder/ai-gateway/cost-controls#configure-model-prices",
+			),
+		);
 
 		const expectedValues: [RegExp, string][] = [
 			[/^input$/i, "3"],

site/src/pages/AISettingsPage/ModelsPage/components/ModelFormFields.tsx

@@ -1,7 +1,7 @@
 import type { FormikContextType } from "formik";
 import { ChevronDownIcon, ChevronRightIcon, InfoIcon } from "lucide-react";
 import type { FC, ReactNode } from "react";
-import { Link } from "react-router";
+import { Link as RouterLink } from "react-router";
 import { getVisibleProviderFields } from "#/api/chatModelOptions";
 import type * as TypesGen from "#/api/typesGenerated";
 import { Button } from "#/components/Button/Button";
@@ -18,6 +18,7 @@ import {
 	InputGroupInput,
 } from "#/components/InputGroup/InputGroup";
 import { Label } from "#/components/Label/Label";
+import { Link } from "#/components/Link/Link";
 import { Spinner } from "#/components/Spinner/Spinner";
 import {
 	Tooltip,
@@ -37,12 +38,13 @@ import type {
 	ModelFormValues,
 } from "#/pages/AgentsPage/components/ChatModelAdminPanel/modelConfigFormLogic";
 import { cn } from "#/utils/cn";
+import { docs } from "#/utils/docs";
 import type { FormHelpers } from "#/utils/formUtils";
 import { ModelFormProviderSelect } from "./ModelFormProviderSelect";
 
 const CollapsibleSection: FC<{
 	title: string;
-	description: string;
+	description: ReactNode;
 	open: boolean;
 	onOpenChange: (open: boolean) => void;
 	className?: string;
@@ -246,7 +248,20 @@ export const ModelFormFields: FC<{
 				<div className="overflow-hidden rounded-lg border border-solid border-border">
 					<CollapsibleSection
 						title="Cost estimate"
-						description="Estimated price per million tokens in USD. Prices are read-only."
+						description={
+							<>
+								Estimated price per million tokens in USD. Prices are read-only.{" "}
+								Model prices are managed by AI Gateway.{" "}
+								<Link
+									href={docs(
+										"/ai-coder/ai-gateway/cost-controls#configure-model-prices",
+									)}
+									size="sm"
+								>
+									Learn how to configure model prices.
+								</Link>
+							</>
+						}
 						open={showCostEstimate}
 						onOpenChange={setShowCostEstimate}
 						contentClassName="grid grid-cols-2 gap-3 pt-3 pl-6 sm:grid-cols-4"
@@ -342,11 +357,11 @@ export const ModelFormFields: FC<{
 				</div>
 
 				<div className="flex items-center justify-end gap-3">
-					<Link to="/ai/settings/models">
+					<RouterLink to="/ai/settings/models">
 						<Button variant="outline" type="button">
 							Cancel
 						</Button>
-					</Link>
+					</RouterLink>
 					<Button type="submit" disabled={!canSubmit}>
 						{isSaving && <Spinner loading />}
 						{isEditing