fix(#375): resolve lint errors in usage dashboard

- Fix prettier formatting for Tooltip formatter props (single-line)
- Fix no-base-to-string by using typed props instead of Record<string, unknown>
- Fix restrict-template-expressions by wrapping number in String()

Refs #375

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/app/(authenticated)/usage/page.tsx

@@ -367,9 +367,7 @@ export default function UsagePage(): ReactElement {
                         width={140}
                       />
                       <Tooltip
-                        formatter={
+                        formatter={((value: number) => [formatCurrency(value), "Cost"]) as never}
-                          ((value: number) => [formatCurrency(value), "Cost"]) as never
-                        }
                         contentStyle={{
                           borderRadius: "8px",
                           border: "1px solid #E2E8F0",
@@ -406,14 +404,12 @@ export default function UsagePage(): ReactElement {
                         dataKey="count"
                         nameKey="outcome"
                         label={
-                          ((props: Record<string, unknown>) =>
+                          ((props: { outcome?: string; count?: number }) =>
-                            `${String(props.outcome ?? "")}: ${String(props.count ?? 0)}`) as never
+                            `${props.outcome ?? ""}: ${String(props.count ?? 0)}`) as never
                         }
                       />
                       <Tooltip
-                        formatter={
+                        formatter={((value: number, name: string) => [value, name]) as never}
-                          ((value: number, name: string) => [value, name]) as never
-                        }
                         contentStyle={{
                           borderRadius: "8px",
                           border: "1px solid #E2E8F0",