feat(import): show character counts and a Preview busy state

The JSON and CSV paste boxes now cap input at the 16 MB body ceiling the
routes enforce and show a live character count beneath each, so an over-long
paste is bounded with feedback instead of silently rejected at submit. The
CSV Preview button also renders the same spinner the Import button does while
a dry-run is in flight, with motion-reduce honoured, so the tap no longer
looks inert on a slow preview.

messages/de.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Import",
           "description": "Importiere Daten aus einem Apple-Health-Export oder einer JSON-Datei. Bereits vorhandene Einträge werden übersprungen, ein erneuter Import ist also unbedenklich.",
+          "charCount": "{used} / {max} Zeichen",
           "appleHealth": {
             "title": "Apple Health",
             "description": "Lade die export.zip aus der Health-App auf dem iPhone hoch (Profil → Alle Gesundheitsdaten exportieren).",

messages/en.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Import",
           "description": "Bring data into HealthLog from an Apple Health export, a JSON file, or a CSV. Imports skip rows that already exist, so re-running one is safe.",
+          "charCount": "{used} / {max} characters",
           "appleHealth": {
             "title": "Apple Health",
             "description": "Upload the export.zip from the Health app on iPhone (Profile → Export All Health Data).",

messages/es.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Importar",
           "description": "Importa datos a HealthLog desde una exportación de Apple Health o un archivo JSON. La importación omite las filas que ya existen, así que repetirla es seguro.",
+          "charCount": "{used} / {max} caracteres",
           "appleHealth": {
             "title": "Apple Health",
             "description": "Sube el archivo export.zip de la app Salud del iPhone (Perfil → Exportar todos los datos de salud).",

messages/fr.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Import",
           "description": "Importez des données dans HealthLog depuis un export Apple Santé ou un fichier JSON. L'import ignore les lignes déjà présentes : le relancer est sans risque.",
+          "charCount": "{used} / {max} caractères",
           "appleHealth": {
             "title": "Apple Santé",
             "description": "Importez le fichier export.zip de l'app Santé sur iPhone (Profil → Exporter toutes les données de santé).",

messages/it.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Importa",
           "description": "Importa dati in HealthLog da un'esportazione di Apple Salute o da un file JSON. L'importazione salta le righe già presenti, quindi ripeterla è sicuro.",
+          "charCount": "{used} / {max} caratteri",
           "appleHealth": {
             "title": "Apple Salute",
             "description": "Carica il file export.zip dall'app Salute su iPhone (Profilo → Esporta tutti i dati sanitari).",

messages/pl.json

@@ -4006,6 +4006,7 @@
         "import": {
           "heading": "Import",
           "description": "Zaimportuj dane do HealthLog z eksportu Apple Health lub pliku JSON. Import pomija wiersze, które już istnieją, więc ponowne uruchomienie jest bezpieczne.",
+          "charCount": "{used} / {max} znaków",
           "appleHealth": {
             "title": "Apple Health",
             "description": "Prześlij plik export.zip z aplikacji Zdrowie na iPhonie (Profil → Eksportuj wszystkie dane zdrowotne).",

src/components/settings/import-panel.tsx

@@ -48,6 +48,13 @@ import { cn } from "@/lib/utils";
 import { apiFetchRaw, apiGet } from "@/lib/api/api-fetch";
 import { CSV_EXAMPLE_COLUMNS } from "@/lib/import/csv-measurements";
 
+/**
+ * Upper bound for the paste textareas, mirroring the 16 MB server-side body
+ * ceiling on `/api/import` and `/api/import/csv`. Caps an accidental over-paste
+ * before it ever reaches the route and feeds the live character counter.
+ */
+const MAX_PASTE_CHARS = 16 * 1024 * 1024;
+
 // ─────────────────────────── Section wrapper ───────────────────────────
 
 export function ImportPanel() {
@@ -537,10 +544,17 @@ function JsonImportCard() {
           value={text}
           onChange={(e) => setText(e.target.value)}
           rows={5}
+          maxLength={MAX_PASTE_CHARS}
           spellCheck={false}
           placeholder='{"measurements":[…],"moodEntries":[…]}'
           className="font-mono text-xs"
         />
+        <p className="text-muted-foreground text-right text-xs tabular-nums">
+          {t("settings.sections.export.import.charCount", {
+            used: text.length,
+            max: MAX_PASTE_CHARS,
+          })}
+        </p>
       </div>
 
       <input
@@ -762,10 +776,17 @@ function CsvImportCard() {
           value={text}
           onChange={(e) => setText(e.target.value)}
           rows={5}
+          maxLength={MAX_PASTE_CHARS}
           spellCheck={false}
           placeholder="type,value,unit,measuredAt,…"
           className="font-mono text-xs"
         />
+        <p className="text-muted-foreground text-right text-xs tabular-nums">
+          {t("settings.sections.export.import.charCount", {
+            used: text.length,
+            max: MAX_PASTE_CHARS,
+          })}
+        </p>
       </div>
 
       <input
@@ -865,6 +886,9 @@ function CsvImportCard() {
           onClick={() => void send(true)}
           data-testid="import-csv-preview"
         >
+          {busy && (
+            <Loader2 className="h-3.5 w-3.5 animate-spin motion-reduce:animate-none" />
+          )}
           {t("settings.sections.export.import.csv.preview")}
         </Button>
         <Button