[ayuxy027]

What was broken

Three small things in the iOS and Android app that hid the real failure from the user:

• Importing a PDF. If the upload failed with a response that isn't JSON (a proxy error page, a gateway timeout, an empty body), the app showed a confusing "Unexpected token" error instead of what actually went wrong.
• Sharing a PDF. If the download failed (an expired session, a deleted file), the app saved the server's error message as the PDF and opened the share sheet with it, so it looked like it worked.
• Event time zone. While you type a time zone, the editor shows "Choose a valid time zone." The message stayed there even after the zone was corrected. And if you changed the date or time while the zone was still invalid, that date and time were never converted, and the editor showed the browser's raw "Invalid time zone specified" text instead.

What happens now

• A failed import shows the server's error, or "Could not import this PDF." This now goes through the same response helper the web upload already uses.
• A failed share shows the server's error, or "Could not download this PDF.", removes the bad file, and doesn't open the share sheet.
• As soon as the zone is valid, the message disappears and a date or time entered in the meantime is converted. An unknown zone always shows "Choose a valid time zone."

How I checked

• Added tests for the native response handling: a normal response, a server error with a message, and an HTML or empty error page.
• pnpm lint, pnpm typecheck and pnpm test pass.
• Not tested on a physical iOS or Android device. The time zone fix has no automated test, since the test setup doesn't render components.

Each fix is a separate commit.