Adds the ability to configure a custom base URL for the PostHog API, e.g. data regions EU or US or self-hosted.

This allows users to specify a different PostHog instance or a proxy server to be used for API requests.

Validates that the base URL ends with `/api/projects/` and persists it in the configuration.
The API key and base URL are now required for the system to be considered fully ready.

Improves user experience by providing a placeholder
value for the base URL input field, guiding the user
on the expected format.

Adds the stored Wi-Fi SSID to the device configuration for
pre-selection in the captive portal UI, enhancing user experience.
The password field is masked for security.

Converts form submission functions to use async/await for improved readability and error handling.
Adds try/catch blocks to handle potential errors during fetch requests, displaying an error message to the user.

The 'refreshNetworks' function now accepts config to preselect SSID if available.

Modifies form submission handlers to prevent default form
submission, ensuring JavaScript functions handle the
submission process. This change avoids unexpected page
reloads and ensures proper form data handling.