fix(wasm): unlock before listening for topics

[HaoboGu]

What

Delay the demo's topic listener until the unlock ceremony has completed. Already-unlocked and permanently locked devices still start the listener immediately.

Why

On a normally locked device, the demo started next_event() and then exposed the unlock button. The pending wasm-bindgen call keeps a mutable borrow of the Rust client, so clicking Unlock re-enters the same object and traps with recursive use of an object detected.

Root cause

The same WasmClient was used concurrently by the indefinitely pending topic pump and the unlock request sequence.

Impact

This only changes demo sequencing. Protocol and firmware behavior are unchanged.

Checks

• Reproduced the pre-fix trap with the generated wasm-bindgen package and a locked-device transport.
• Extracted module passes node --input-type=module --check.

Built on #848.