AP provisioning + fast_connect

**Describe the problem you have/What new integration you would like**

From what I understand it is not possible to use AP provisioning (no SSID/PW specified) and also use fast_connect, or is there a workaround?

I am making a device that will sleep most of the time, on battery, thus I want fast_connect.
However, I want it to ship with ESPHome code and no specified SSID/PW.

If I dont specify SSID/PW, there will be an error when enabling fast_connect.

Once the SSID/PW provisioning is done, why would it not be possible to use fast_connect?

**Please describe your use case for this integration and alternatives you've tried:**

**Additional context**

Start by tracing ESPHome's AP provisioning flow and the fast_connect validation that rejects configurations without an SSID or password. Determine whether fast_connect can be enabled after provisioning, and define the expected behavior for a device shipped without Wi-Fi credentials. Done should include support for both features together or a documented workaround.

Written by the indexing model from the issue text.