fix(forms): send one Idempotency-Key per opened create form

A mood, symptom, lab value, custom metric value, unscheduled dose,
allergy, vaccination, visit or measurement saved on a weak signal could
be stored twice: the POST committed, the answer missed the 15 s
timeout, the form said it could not save, and the second tap was a new
call with a new key, so the server ran it again.

useIdempotentPost keeps one key until a save lands and renews it for the
next entry, so the retry replays the first answer. The create forms and
the three create hooks post through it; the comment on the per-call key
in api-fetch now says what that key does and does not cover.

LabForm and MoodForm each gain the one line that mounts the key, so
their function-size baselines go up by one. The intake toast guard now
recognises a dose posted through the hook.

src/components/records/allergy-form.tsx

@@ -17,7 +17,8 @@ import {
   SelectValue,
 } from "@/components/ui/select";
 import { Textarea } from "@/components/ui/textarea";
-import { apiPost, apiPut } from "@/lib/api/api-fetch";
+import { apiPut } from "@/lib/api/api-fetch";
+import { useIdempotentPost } from "@/lib/api/use-idempotent-post";
 import { localizedApiError } from "@/lib/api/localized-error";
 import {
   allergyCategoryEnum,
@@ -67,6 +68,7 @@ export function AllergyForm({
   footerSlot,
 }: AllergyFormProps) {
   const { t } = useTranslations();
+  const post = useIdempotentPost();
   const formId = useId();
 
   const [substance, setSubstance] = useState(existing?.substance ?? "");
@@ -106,7 +108,7 @@ export function AllergyForm({
     try {
       const saved = existing
         ? await apiPut<AllergyDTO>(`/api/allergies/${existing.id}`, body)
-        : await apiPost<AllergyDTO>("/api/allergies", body);
+        : await post<AllergyDTO>("/api/allergies", body);
       toast.success(
         existing
           ? t("records.allergies.form.updatedToast")