feat: add FormNumberStepper to medication edit forms (#274)

Replace plain numeric inputs with a reusable +/− stepper component in
both desktop (MedicationsPage) and mobile (MobileEditModal) edit forms.

Applied to Stock, Schedule, and Prescription tab fields. Reorder tabs
so Schedule appears before Prescription. Add responsive grid overrides
for narrow sidebar and compact schedule rows.

Fix label-hover ghost activation by placing <input> first in DOM
(CSS order restores visual [−] [value] [+] layout).

Closes #273

frontend/src/components/index.ts

@@ -6,6 +6,7 @@ export { ConfirmModal } from "./ConfirmModal";
 export { DateInput } from "./DateInput";
 export { DateTimeInput } from "./DateTimeInput";
 export { default as ExportModal } from "./ExportModal";
+export { FormNumberStepper } from "./FormNumberStepper";
 export type { LightboxProps } from "./Lightbox";
 
 export { Lightbox } from "./Lightbox";