Fix OpenCV tracker hang: handle Promise-based WASM export and add timeout

[veillette]

The @techstark/opencv-js package (v4.12.0+) can export its default as a
Promise. The previous loadCV() did not handle this case — it set
onRuntimeInitialized on the Promise object itself, which never fires,
causing the tracker to hang indefinitely.

• Await the default export when it is a Promise
• Add a 30 s timeout on WASM initialisation so it rejects instead of
  hanging forever
• Clear the cached promise on failure so retries are possible
• Attach .catch() to the fire-and-forget initFromVideo() call so
  failures surface in the console and re-show the hint text
• Wrap Mat operations in try/finally to prevent WASM memory leaks if
  OpenCV throws mid-operation

https://claude.ai/code/session_014aYixwNeB8Fx1jWz9AyXUD