[N3b3x]

Summary

Corrects the layer table on the Architecture page and links the HardFOC engineering standard from it and from the Contribute page.

Why

Parts of the layer table were wrong:

• Interface wrap was described as depending on ESP-IDF with ESP-IDF implementations only. Its base classes are platform-free, and it has STM32 (STM32 HAL) and host implementations as well as ESP32.
• Utilities were described as header-only helpers and FreeRTOS wrappers. hf-utils-general and hf-utils-canopen have source files, and hf-utils-rtos-wrap has FreeRTOS, CMSIS-RTOS2, ThreadX and no-RTOS backends.
• The last column was headed "Platform code" but listed what each layer contains; it is now "Contains", and the rows say what each layer holds (handlers, the facade and bind, MCU-bound drivers).

The design review asked for this page to become the stack contract, so it now has a section that links the standard's layer, error, threading and per-layer contract pages and the ADRs.

The figure region is unchanged.

The links point at standards/ in hardfoc/.github, added by hardfoc/.github#11, and resolve once that PR merges. Merge that one first.

How verified

• CI green (strict build, link check, Lighthouse)
• markdownlint clean on the two changed pages
• On target: n/a