Exit bootloader and jump to app when USB is disconnected

[jesuslg123]

Description of Change

Summary

This PR updates bootloader startup behavior so it automatically jumps to the application in specific USB-related cases, provided the application is valid.

New behavior

The bootloader now jumps to the app when:

• USB is not enumerated within 3 seconds during boot.
  • If no USB host enumerates the device in that window, the bootloader times out and starts the app.
• USB was enumerated during startup, but is later physically disconnected.
  • In that case, the bootloader exits startup DFU and starts the app.

In both cases, the jump only happens if a valid application is present.

Behavior that does not change

This auto-jump logic does not apply to DFU flows that are intended to keep the device in DFU mode, including:

• Double-reset DFU
• DFU button entry, or DFU+OTA button entry
• OTA/BLE DFU
• Any path that calls bootloader_dfu_start(..., 0, false)

Rationale

This makes USB-startup DFU less sticky for normal boot scenarios: if a host never enumerates the device, or if the USB cable is disconnected after enumeration, the device can continue into the main application automatically instead of remaining in the bootloader unnecessarily.