Reusable BSP Framework (Abstract BSP Interface & NUCLEO_F401RE Migration)

[AmmarOkla12772]

Introduce a hardware-independent BSP interface and migrate the NUCLEO_F401RE target to use it, allowing shared applications to build without depending on board-specific headers.

Goals:

• Define common BSP interface headers.
• Implement the BSP interface for NUCLEO_F401RE.
• Move the ThreadX demo into the shared application directory.
• Replace direct vendor dependencies with BSP interface calls.
• Document board-specific configuration.

DoD:

• Shared application builds successfully for NUCLEO_F401RE.
• Existing demo functionality remains unchanged.
• LED, UART, and ThreadX operation are validated on hardware.