fix(build): extract STORED_LOGO_SENTINEL to non-server module

Vite/React Router refused to bundle the client because
app/routes/app.settings.tsx imported the constant from a .server file
and used it inside the route component (not just loader/action), so it
could not be tree-shaken out.

Move the sentinel to logoCache.constants.ts, re-export from
logoCache.server.ts for backwards compatibility, and import the constant
from constants in the route while keeping the server-only functions
(deleteStoredLogo, storeUploadedLogo) imported from .server (they are
only referenced inside the action and get tree-shaken correctly).

app/services/invoice/logoCache.server.ts

@@ -1,4 +1,5 @@
 import db from "../../db.server";
+import { STORED_LOGO_SENTINEL } from "./logoCache.constants";
 
 const MAX_BYTES = 5 * 1024 * 1024; // 5 MB cap
 const STALE_AFTER_MS = 24 * 60 * 60 * 1000; // re-fetch once a day at most
@@ -7,8 +8,11 @@ const STALE_AFTER_MS = 24 * 60 * 60 * 1000; // re-fetch once a day at most
  * Sentinel value stored in `ShopSettings.logoUrl` when the logo was uploaded
  * directly through the settings UI (rather than fetched from a remote URL).
  * The actual bytes live in `LogoCache` for that shop.
+ *
+ * Re-exported from `logoCache.constants` so existing server-side imports keep
+ * working; new client/route imports should use `logoCache.constants` directly.
  */
-export const STORED_LOGO_SENTINEL = "stored://shop-logo";
+export { STORED_LOGO_SENTINEL };
 
 /**
  * Returns a `data:` URL for the shop's logo bytes, fetching from the