feat(ares): ARES company lookup with prefill in customer/supplier modals

New /api/admin/ares proxy (browser cannot reach ares.gov.cz - CORS+CSP):
GET /ico/:ico and GET /search?q= map the MFCR REST API to the form
shape (street incl. orientation numbers, "511 01" PSC format, DIC).
Guarded by customers.create/edit + warehouse.manage; token errors map
to Czech messages. Shared AresAdornment button sits in the Nazev and
ICO fields of both modals: ICO mode fills directly, name mode searches
with a result picker. Tested against live ARES (BOHA, ICO 22599851).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/components/AresLookup.tsx

@@ -0,0 +1,153 @@
+import { useState, useRef } from "react";
+import InputAdornment from "@mui/material/InputAdornment";
+import IconButton from "@mui/material/IconButton";
+import Tooltip from "@mui/material/Tooltip";
+import Menu from "@mui/material/Menu";
+import MenuItem from "@mui/material/MenuItem";
+import Typography from "@mui/material/Typography";
+import Box from "@mui/material/Box";
+import CircularProgress from "@mui/material/CircularProgress";
+import { jsonQuery } from "../lib/apiAdapter";
+import { useAlert } from "../context/AlertContext";
+
+/** Normalized company record returned by the /api/admin/ares proxy. */
+export interface AresCompany {
+  ico: string;
+  dic: string | null;
+  name: string;
+  street: string;
+  city: string;
+  postal_code: string;
+  country: string;
+}
+
+interface AresAdornmentProps {
+  /** "ico" looks the query up directly; "name" searches and offers a picker. */
+  mode: "ico" | "name";
+  /** Current value of the host field (IČO or name fragment). */
+  query: string;
+  /** Called with the chosen company — the modal prefills its form from it. */
+  onFill: (company: AresCompany) => void;
+}
+
+/**
+ * "ARES" end-adornment button for the Název/IČO fields of the customer and
+ * supplier modals. IČO mode fetches the subject directly; name mode searches
+ * ARES and shows a result picker (filling straight away on a single hit).
+ * Pass via the TextField's `InputProps.endAdornment`.
+ */
+export default function AresAdornment({
+  mode,
+  query,
+  onFill,
+}: AresAdornmentProps) {
+  const alert = useAlert();
+  const [loading, setLoading] = useState(false);
+  const [results, setResults] = useState<AresCompany[]>([]);
+  const [menuOpen, setMenuOpen] = useState(false);
+  const anchorRef = useRef<HTMLButtonElement | null>(null);
+
+  const trimmed = query.trim();
+  const enabled =
+    mode === "ico"
+      ? /^\d{8}$/.test(trimmed.replace(/\s+/g, ""))
+      : trimmed.length >= 2;
+  const tooltip =
+    mode === "ico"
+      ? enabled
+        ? "Načíst údaje z ARES podle IČO"
+        : "Vyplňte 8místné IČO"
+      : enabled
+        ? "Vyhledat firmu v ARES podle názvu"
+        : "Vyplňte alespoň 2 znaky názvu";
+
+  const lookup = async () => {
+    if (!enabled || loading) return;
+    setLoading(true);
+    try {
+      if (mode === "ico") {
+        const company = await jsonQuery<AresCompany>(
+          `/api/admin/ares/ico/${encodeURIComponent(trimmed.replace(/\s+/g, ""))}`,
+        );
+        onFill(company);
+      } else {
+        const found = await jsonQuery<AresCompany[]>(
+          `/api/admin/ares/search?q=${encodeURIComponent(trimmed)}`,
+        );
+        if (found.length === 0) {
+          alert.error("Žádná firma tohoto názvu nebyla v ARES nalezena");
+        } else if (found.length === 1) {
+          onFill(found[0]);
+        } else {
+          setResults(found);
+          setMenuOpen(true);
+        }
+      }
+    } catch (e) {
+      alert.error(
+        e instanceof Error ? e.message : "Registr ARES je nedostupný",
+      );
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  return (
+    <InputAdornment position="end">
+      <Tooltip title={tooltip}>
+        <span>
+          <IconButton
+            ref={anchorRef}
+            size="small"
+            onClick={lookup}
+            disabled={!enabled || loading}
+            aria-label="Načíst z ARES"
+            edge="end"
+          >
+            {loading ? (
+              <CircularProgress size={16} color="inherit" />
+            ) : (
+              <Typography
+                component="span"
+                sx={{
+                  fontSize: "0.65rem",
+                  fontWeight: 800,
+                  letterSpacing: "0.06em",
+                  color: enabled ? "primary.main" : "text.disabled",
+                  lineHeight: 1,
+                }}
+              >
+                ARES
+              </Typography>
+            )}
+          </IconButton>
+        </span>
+      </Tooltip>
+      <Menu
+        anchorEl={anchorRef.current}
+        open={menuOpen}
+        onClose={() => setMenuOpen(false)}
+      >
+        {results.map((c) => (
+          <MenuItem
+            key={c.ico}
+            onClick={() => {
+              setMenuOpen(false);
+              onFill(c);
+            }}
+          >
+            <Box>
+              <Typography variant="body2" sx={{ fontWeight: 600 }}>
+                {c.name}
+              </Typography>
+              <Typography variant="caption" color="text.secondary">
+                IČO {c.ico}
+                {c.city ? ` · ${c.city}` : ""}
+              </Typography>
+            </Box>
+          </MenuItem>
+        ))}
+      </Menu>
+    </InputAdornment>
+  );
+}

src/admin/pages/OffersCustomers.tsx

@@ -12,6 +12,7 @@ import {
   type CustomField,
 } from "../lib/queries/offers";
 import { useApiMutation } from "../lib/queries/mutations";
+import AresAdornment, { type AresCompany } from "../components/AresLookup";
 import {
   Button,
   Card,
@@ -267,6 +268,21 @@ export default function OffersCustomers() {
     return key;
   };
 
+  // ARES prefill — overwrite the company fields with registry data (the
+  // button is an explicit user action, so overwriting is the expected UX).
+  const fillFromAres = (c: AresCompany) => {
+    setForm((prev) => ({
+      ...prev,
+      name: c.name || prev.name,
+      street: c.street,
+      city: c.city,
+      postal_code: c.postal_code,
+      country: c.country,
+      company_id: c.ico,
+      vat_id: c.dic || "",
+    }));
+  };
+
   const openCreateModal = () => {
     setEditingCustomer(null);
     setForm({
@@ -535,6 +551,15 @@ export default function OffersCustomers() {
               setForm((prev) => ({ ...prev, name: e.target.value }))
             }
             placeholder="Název firmy / jméno"
+            InputProps={{
+              endAdornment: (
+                <AresAdornment
+                  mode="name"
+                  query={form.name}
+                  onFill={fillFromAres}
+                />
+              ),
+            }}
           />
         </Field>
         <Field label="Ulice">
@@ -596,6 +621,15 @@ export default function OffersCustomers() {
                   company_id: e.target.value,
                 }))
               }
+              InputProps={{
+                endAdornment: (
+                  <AresAdornment
+                    mode="ico"
+                    query={form.company_id}
+                    onFill={fillFromAres}
+                  />
+                ),
+              }}
             />
           </Field>
           <Field label="DIČ">