feat: GPU process list with per-process VRAM/utilization and kill

Add a GPU process table to the Performance tab showing which processes
use the selected GPU, with per-process VRAM, GPU utilization, CPU, host
memory, and command. Includes a kill endpoint (SIGTERM/SIGKILL, with
optional parent kill) behind a confirm dialog.

- nvcurve/hal/processes.py: NVML + /proc process enumeration
- server.py: GET /api/processes, POST /api/processes/kill (refuses to
  signal init/kthreadd)
- frontend: ProcessList component, API client, types
- tests: test_processes.py
- docs: API reference for the new endpoints

Makefile

@@ -26,6 +26,7 @@ test: ## Run the test suite
 	$(UV) run python tests/test_security.py
 	$(UV) run python tests/test_rm_power.py
 	$(UV) run python tests/test_wireview.py
+	$(UV) run python tests/test_processes.py
 
 clean: ## Remove build artifacts
 	rm -rf frontend/dist frontend/node_modules