[youtalk]

First of several stacked PRs implementing the Phase 2 plan tracked in #14 (vendored upstream + rclcpp facade over micro-ROS, verified on a FreeRTOS POSIX simulator). Builds on the FreeRTOS PAL direction in #1.

Summary

• Adds external/FreeRTOS-Kernel as a git submodule pinned to V11.1.0 (commit dbf70559b).
• Adds freertos/FreeRTOSConfig.h tuned for the 64-bit POSIX port (16 MiB heap, mutex/timer config, malloc/stack-overflow hooks, custom assert).
• Adds a minimal freertos/CMakeLists.txt with a freertos_kernel static library (FreeRTOS-Kernel + POSIX port + heap_4) and a hello_freertos executable that prints hello freertos from a FreeRTOS task.

The existing Zephyr build (./build.sh -t fvp_baser_aemv8r_smp) is untouched by this PR: only new files under freertos/ and external/FreeRTOS-Kernel/ are added.

Test plan

• cmake -S freertos -B build/freertos && cmake --build build/freertos — green from a clean state.
• timeout 1s ./build/freertos/hello_freertos — prints hello freertos from inside a FreeRTOS task on the POSIX scheduler.

Stack

• This PR (Stage 0).
• Phase 2 / Stage 1-2 follows, stacked on this branch.
• Phase 2 / Stage 3, 4, 5-7 follow in turn.