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.

README

@@ -2,6 +2,113 @@ G15Stats - a CPU/Memory/Swap/Network/Battery/Temperature/Fan Speed/CPU Frequenci
 
 The G15Stats requires libgtop development packages to be installed before compilation.
 
+GPU summary columns:
+The default --gpu auto collects ALL PCI devices (sorted PCI address) bound
+to amdgpu or nvidia at startup, including mixed vendors. Use --gpu dddd:bb:ss.f (also -gpu), for example
+--gpu 0000:01:00.0, to select a particular card. --gpu off restores the original
+layout and disables collection. An explicit missing/unsupported card shows N/A;
+auto with no supported card leaves the original layout unchanged. Restart to
+rediscover cards after hotplug. Intel and the nouveau/radeon drivers are not
+supported. Missing tools, permissions or individual metrics produce N/A, not 0.
+
+With one GPU the 160x43 summary retains its existing 4/5 indicator rows and
+labels. Graphs end at x=96 instead of 153; TOTAL moves to x=98. A divider
+at x=105 separates the column at x=108..159. With two or more GPUs the left
+x=0..50 shows compact CPU percent, R used system RAM, T total system RAM,
+SWP percent, and (in five-row mode) GPU count. Four-row mode uses y=1,10,19,28;
+five-row mode uses y=1,8,15,22,29. System RAM uses the same explicit units as VRAM.
+Two GPU columns at x=54..104 and x=108..159 are visible together, with dividers
+at x=51 and x=105 (the first column's glyphs end before its right divider).
+Each GPU has five lines at y=1,8,15,22,29: vendor/index plus PCI bus:slot.function,
+UTL percent, U used VRAM, T total VRAM, TEM temperature in Celsius (C).
+For example NV1 01:00.0 and AMD2 11:00.0 identify different cards. Indices are
+one-based positions in the selected PCI-sorted inventory, not NVIDIA ordinals;
+startup diagnostics map each index to its full domain:bus:slot.function address.
+More than two GPUs cycle through consecutive pairs every five seconds from
+startup (1/2, 3/4, ..., then 1/2); the last odd card occupies the first column.
+All cards are collected continuously, not just the visible pair. The display
+refresh interval can delay a page change: each draw advances at most one pair,
+so slow refresh never skips pairs. Inventory is bounded at 64 cards;
+overflow/enumeration failure is an explicit startup error, never silent omission.
+Use explicit PCI selection or off to recover. Hotplug requires restart.
+The bottom info bar at y=37..42 and all non-summary screens retain their geometry.
+Used and total are on separate lines so each retains an explicit MiB/GiB unit
+(TiB/PiB for very large values), rounded to one decimal. Other screens do not
+change. U/T refer to VRAM, not memory-controller utilization or system RAM;
+on AMD APUs the driver may report only the reserved VRAM carveout.
+
+AMD reads gpu_busy_percent, mem_info_vram_used/total (bytes), and the selected
+PCI device's hwmon/temp1_input (millidegrees C). NVIDIA optionally executes
+/usr/bin/nvidia-smi with pci.bus_id,utilization.gpu,memory.used,memory.total,temperature.gpu
+and --format=csv,noheader,nounits: one query for all NVIDIA cards, matched by PCI
+identity (including NVIDIA's eight-digit domain form), not response order. No CUDA/NVML SDK
+or additional build dependency is needed. Run as an ordinary user.
+
+Independent AMD workers and one batched NVIDIA worker wait two seconds between
+queries; drawing uses only a mutex-protected snapshot array. A stalled AMD read
+does not block another card or NVIDIA. NVIDIA queries share one 750ms monotonic deadline, fixed
+arguments/environment, no shell, bounded output, and SIGKILL on timeout or
+parent death. An unreaped child prevents further launches. Samples older than
+five seconds display N/A per card, including when a sysfs read stalls. Worker
+shutdown has one shared one-second join/reap budget; a stuck kernel read can
+outlive that budget in static storage until process exit (no restart after a
+failed stop). Normal application termination exits the process; no driver waits
+are added to signal handling. The -r display
+refresh interval still applies independently. No GPU settings are written.
+
+Official interface references:
+https://docs.kernel.org/gpu/amdgpu/thermal.html
+https://docs.kernel.org/gpu/amdgpu/driver-misc.html
+https://docs.nvidia.com/deploy/nvidia-smi/index.html
+
+GPU validation:
+After configuring/building, make check runs compiled parsing, units, missing-data,
+expiry, selection, subprocess deadline/reaping/parent-death and descriptor checks,
+plus real libg15render buffer checks. No daemon, input devices or synthetic GPU
+sysfs fixtures are used. ./gpu-test auto additionally checks every real GPU,
+its sysfs vendor identity and background cache (requires all four metrics).
+Explicit PCI arguments still test one card. ./render-test auto output writes
+real live 160x43 buffers to output-0.pgm and output-1.pgm (five/four rows), plus
+output (four rows). ./render-test off output renders the original GPU-off layout.
+For in-memory cases, ./render-test off output COUNT PAGE [large|unknown] selects
+1..64 cards and a zero-based pair page. Omit PAGE to export the last pair.
+The default values exercise LLONG_MAX VRAM and -273C/1000C; large uses
+100.0/192.0GiB and 1000C, while unknown uses N/A for all GPU metrics.
+For example ./render-test off output 2 tests worst-width dual-card values;
+./render-test off output 3 1 tests the odd last page. With no arguments,
+make check retains the worst-width two-card case. These are rendering inputs,
+not simulated hardware or claims about the installed GPUs.
+These do not connect to g15daemon and are not physical LCD tests.
+
+make check also runs tests/render-layouts.sh for off, single, dual, large,
+unknown, odd-last and 64-card layouts, each in both summary modes. In addition
+to isolated-column comparisons, the test compares final GPU text, vertical
+TOTAL and time-footer cells directly with the installed font's bitmap bits.
+This independent oracle includes blank cells and checks full glyph bounds;
+repeating renderString on another canvas alone cannot detect shared clipping.
+Canvas initialization is tested starting from poisoned storage.
+
+Startup regression: make check also runs runtime-test through the full main
+loop for three frames with real libgtop and bitmap rendering. Only daemon
+transport is replaced by a private socketpair; no keyboard events are sent.
+./runtime-test auto 21 additionally requires valid live GPU samples after
+twenty seconds. This is not a physical LCD or real daemon integration test.
+The bitmap-only client initializes its own canvas, avoiding g15r_initCanvas:
+a TTF-enabled renderer can otherwise write beyond a non-TTF caller's canvas
+and corrupt malloc metadata at startup, even with --gpu off.
+
+Each visual export also writes output-0.bin and output-1.bin: the actual 860
+packed framebuffer bytes (one means black). With ImageMagick installed, run
+sh tests/render-images.sh /absolute/output/directory after generating frames
+there. It compares packed PBM, PGM and native PNG pixels, generates exact
+nearest-neighbor 8x images, and checks the 8x-to-native round trip. Per-scenario
+contact sheets use 4x tiles with labels outside the LCD and one column, avoiding
+very wide sheets that viewers may downscale. No trim or crop is applied.
+Inspect the individual native and 8x files as well as the contact sheets.
+The supplied default small font has only three ink columns plus a blank column
+per character; its N, M and other shapes can look incomplete when enlarged.
+Use the bitmap checks to distinguish those font shapes from missing pixels.
+
 Features:
 Summary Screen displays 4 or 5 indicators from CPU/Frequency/Memory/NET/Temperature/Fan Speed/Swap,
  along with current time.