platform: fix FreeRTOS scheduler on Zynq-A9 QEMU

[zevorn]

Summary

Fix three issues that prevented FreeRTOS from scheduling tasks on the Zynq-A9 QEMU platform. After this fix, claw_init() runs to completion with all services initialized.

Root causes

1. Vector table overlap — .freertos_vectors section lacked "ax" flags, so the linker assigned it the same VMA as .text. The IRQ vector at VBAR+0x18 pointed to Xil_In32 instead of FreeRTOS_IRQ_Handler

2. VFP not enabled — vPortRestoreTaskContext uses VPOP {d0-d15} / VPOP {d16-d31} to restore FPU context (configUSE_TASK_FPU_SUPPORT=2), but CP10/CP11 coprocessor access and FPEXC.EN were never set. This caused an Undefined Instruction exception on the first context switch

3. Priority overflow — configMAX_PRIORITIES was 8 but CLAW_GW_THREAD_PRIO and CLAW_AI_WORKER_PRIO are 15, triggering configASSERT(uxPriority < configMAX_PRIORITIES) in xTaskCreate()

Changes

File	Fix
FreeRTOS_asm_vectors.S	Add "ax" flags to .freertos_vectors section
link.ld	Add ALIGN(32) to .freertos_vectors (ARM VBAR requirement)
startup.S	Enable VFP (CPACR CP10/CP11 + FPEXC.EN), run main in SVC mode
FreeRTOSConfig.h	configMAX_PRIORITIES 8 → 32

Boot output after fix

rt-claw: Zynq-A9 QEMU (FreeRTOS) - Real-Time Claw

  +-----------------------------------------+
  |          rt-claw v0.1.0                 |
  |  Real-Time Claw / Swarm Intelligence    |
  +-----------------------------------------+

[I/init] init: gateway
[I/gateway] started / initialized
[I/init] init: sched
[I/init] init: swarm
[I/init] init: net
[I/init] init: tools
[I/init] init: ai_engine
[I/ai] engine ready (model: claude-sonnet-4-6, tools: 1)
[I/init] init: ai_skill
[I/init] start: swarm

Test plan

• make run-zynq-a9-qemu — full boot, all services initialize
• make test-smoke-zynq — boot banner test passes
• Verify ESP32 and vexpress-a9 builds unaffected