Stage 0: org-contact custom fields (Food_Co_op_Organizing)

Adds four fields from the Organization Contact's Food_Co_op_Organizing
custom group to the Stage 0 (always-visible) section:

  Date Incorporated                (date, editable)
  Name on Incorporation Certificate (text, editable)
  Certificate of Incorporation     (readonly; see note)
  Equity share                     (currency, editable)

These live on the Organization Contact record, not on the Check-in
activity, so they read/write through a different code path:

  - FieldConfig gains civiContactField, mutually exclusive with civiField
  - /api/data extends the org Contact.get select to include them and
    merges values into the prefill payload keyed by form-side name
  - /api/submit splits incoming values: contact-bound fields go through
    Contact.update (run first), activity-bound fields stay in the
    Activity.create call (run second)
  - FieldRenderer readonly branch now detects file-shaped values
    ({id, file_name}) and displays the filename rather than [object Object]

Certificate_of_Incorporation is wired readonly only: the form's
file-upload pipeline is not actually wired end-to-end (FileList drops
at JSON.stringify in onSubmit; no /api/upload endpoint exists). A
follow-up will close that gap.

Also adds scripts/inspect-org-custom-fields.mjs, a one-off introspection
script for dumping CustomField metadata when wiring a new group.

components/fields/FieldRenderer.tsx

@@ -66,11 +66,25 @@ export function FieldRenderer({
 
   // ── Readonly display field ──────────────────────────────────────────────
   if (field.type === "readonly") {
-    const opt = effectiveOptions.find((o) => o.value === readonlyValue);
-    const display =
-      readonlyValue == null || readonlyValue === ""
-        ? "—"
-        : opt?.label ?? String(readonlyValue);
+    // File-shaped readonly value: {id, file_name} from a CiviCRM file field
+    // (e.g. Certificate of Incorporation). Render the filename rather than
+    // "[object Object]".
+    let display: string;
+    if (
+      readonlyValue != null &&
+      typeof readonlyValue === "object" &&
+      !Array.isArray(readonlyValue) &&
+      "file_name" in (readonlyValue as Record<string, unknown>)
+    ) {
+      const fn = (readonlyValue as { file_name?: unknown }).file_name;
+      display = typeof fn === "string" && fn ? fn : "Attachment on file";
+    } else {
+      const opt = effectiveOptions.find((o) => o.value === readonlyValue);
+      display =
+        readonlyValue == null || readonlyValue === ""
+          ? "—"
+          : opt?.label ?? String(readonlyValue);
+    }
     return (
       <div className="space-y-1">
         <Label id={id} field={field} />