v0.6.1: stop Anonymous Mode bouncing to sign-in on every foreground

Parking without an account showed "Your session expired — please sign in
again." repeatedly and kicked the user back to the login screen.

The 401 hook on the API client is global: it fires on every unauthorized
response whether or not the caller caught the error. Anonymous Mode has no
token, so any ParkSmarter call 401s, and two of them run automatically —
discoverPaidSession() on open and every foreground, and the map's
lastSessionLot() on every mount. Each one flipped the status to signedOut;
re-entering anonymous mode ran them again, hence "over and over".

Both call sites already caught their errors, which is why this hid: the
bounce came from the client hook, not from the catch.

- A 401 in Anonymous Mode is no longer treated as a session expiry. There is
  no session to expire, and bouncing to sign-in makes the mode pointless.
  This also covers the Sessions/Favorites/Scan tabs, which 401 the same way.
- authBus carries the mode to the non-React modules that need it.
- discoverPaidSession() and lastSessionLot() are skipped entirely when
  anonymous rather than fired and discarded.
- "Last lot" now says it needs an account instead of silently doing nothing.

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

app/src/screens/MapScreen.tsx

@@ -113,6 +113,9 @@ export function MapScreen() {
   // Look up the LAST session's parking-lot coordinate (the meter's own location
   // from history — never the user's GPS). Used to open the map and by "Last lot".
   const lastSessionLot = useCallback(async (): Promise<Coords | null> => {
+    // No account, no session history — and asking anyway 401s, which the global
+    // handler would turn into a bogus "session expired" bounce.
+    if (isAnonymous) return null;
     try {
       const past = await ps.getPastParkingSessions({ currentPage: 1, pageSize: 1 });
       const s = past.Session?.[0] as Record<string, any> | undefined;
@@ -125,7 +128,7 @@ export function MapScreen() {
       /* ignore */
     }
     return null;
-  }, []);
+  }, [isAnonymous]);
 
   // Open on your last parking lot — NOT your GPS. Your location is only ever sent
   // to the API when you explicitly tap "My location", so we never auto-center on it.
@@ -257,6 +260,10 @@ export function MapScreen() {
   // Center on the LAST SESSION's parking lot (the meter's own coordinate from
   // history — never your GPS) and search around it with a ~couple-mile view.
   const searchLastSessionLot = async () => {
+    if (isAnonymous) {
+      setStatus('Sign in to use your last parking lot — it comes from your account history.');
+      return;
+    }
     setLoading(true);
     setStatus('Finding your last parking lot…');
     const lot = await lastSessionLot();