Add mixed-vendor GPU summary and fix startup heap corruption

Collect AMD amdgpu sysfs and optional NVIDIA nvidia-smi stats in the
background, auto-detecting supported adapters in PCI order and rotating
additional pairs alongside CPU/RAM. Explicit PCI selection and off mode
remain supported; missing metrics render as N/A.

Initialize the bitmap-only canvas locally instead of the ABI-dependent
libg15render initializer: the installed TTF-enabled renderer wrote an
8-byte FreeType pointer past the smaller bitmap-only allocation, corrupting
the heap before GPU threads started. Add collector, rendering and full-main
regression tests.

Makefile.am

@@ -11,5 +11,18 @@ LIBS = -lg15daemon_client -lg15render -lpthread -lm -lrt
 IMCLUDES = -I
 g15stats_LDFLAGS = -avoid-version
 g15stats_SOURCES =  g15stats.c g15stats.h
+EXTRA_DIST = gpu.h tests/gpu-test.c tests/render-test.c tests/runtime-test.c tests/render-layouts.sh tests/render-images.sh
+noinst_HEADERS += gpu.h
+AUTOMAKE_OPTIONS = subdir-objects
+check_PROGRAMS = gpu-test render-test runtime-test
+TESTS = $(check_PROGRAMS) tests/render-layouts.sh
+TEST_EXTENSIONS = .sh
+SH_LOG_COMPILER = $(SHELL)
+gpu_test_SOURCES = tests/gpu-test.c
+gpu_test_LDADD = -lpthread
+render_test_SOURCES = tests/render-test.c
+render_test_LDADD = -lg15daemon_client -lg15render -lpthread -lm -lrt $(GTOP_LIBS)
+runtime_test_SOURCES = tests/runtime-test.c
+runtime_test_LDADD = -lg15render -lpthread -lm -lrt $(GTOP_LIBS)