feat(water-log): surface irrigator name on log form + success screen

Makes the currently-signed-in irrigator visible while data is being
entered and confirmed, so the operator can verify the reading is
attributed to them at a glance.

  - LogForm nav bar: title + initials avatar + name as a subtitle,
    sign-out button moves from the form footer into the nav bar
    (more discoverable, frees vertical space for the Submit button)
  - SuccessScreen recap: 'Logged by {name}' row with avatar below
    the timestamp, matches the log form styling
  - MobileWaterApp threads irrigatorName through to both screens

The headgate list still shows 'Signed in as {name}' as a small
caption — left untouched to avoid duplicate UI.

Validation:
  - tsc --noEmit clean
  - eslint clean on all modified files

src/components/water/mobile/SuccessScreen.tsx

@@ -26,6 +26,9 @@ type Props = {
   measurement: number;
   unit: string;
   timestamp: Date;
+  /** Name of the irrigator who logged the entry — shown in the recap
+   *  so the operator can confirm the reading is attributed to them. */
+  irrigatorName?: string;
   onLogAnother: () => void;
   onBackToHeadgates: () => void;
 };
@@ -35,6 +38,7 @@ export function MobileWaterSuccessScreen({
   measurement,
   unit,
   timestamp,
+  irrigatorName,
   onLogAnother,
   onBackToHeadgates,
 }: Props) {
@@ -197,6 +201,17 @@ export function MobileWaterSuccessScreen({
             <div className="mt-2 border-t border-[rgba(60,60,67,0.10)] pt-2 text-[12px] text-[rgba(60,60,67,0.45)]">
               {formatLongTimestamp(timestamp)}
             </div>
+            {irrigatorName ? (
+              <div className="mt-1.5 flex items-center gap-1.5 text-[12px] text-[rgba(60,60,67,0.55)]">
+                <span
+                  aria-hidden
+                  className="inline-flex h-4 w-4 shrink-0 items-center justify-center rounded-full bg-[#14532d] text-[9px] font-bold uppercase text-white"
+                >
+                  {initials(irrigatorName)}
+                </span>
+                <span>Logged by {irrigatorName}</span>
+              </div>
+            ) : null}
           </div>
 
           {/* Action buttons */}
@@ -247,4 +262,16 @@ export function MobileWaterSuccessScreen({
   );
 }
 
-export default MobileWaterSuccessScreen;
+export default MobileWaterSuccessScreen;
+
+/**
+ * Two-letter initials for the avatar chip in the recap.
+ * Mirrors the same helper used in the log form header so the avatar
+ * stays consistent across the two screens.
+ */
+function initials(name: string): string {
+  const parts = name.trim().split(/\s+/).filter(Boolean);
+  if (parts.length === 0) return "?";
+  if (parts.length === 1) return parts[0].slice(0, 2).toUpperCase();
+  return (parts[0][0] + parts[parts.length - 1][0]).toUpperCase();
+}