test: add BATS test suite (79 tests)

- tests/common.bats: PROJECT_ROOT detection, is_cmd, timestamp, data_dir,
  logging functions, color handling, require_root
- tests/detect.bats: GPU sysfs reads with mock sysfs tree, kernel param
  parsing (word boundary, dot escaping, edge positions), recommended
  GTT/pages computation (64GB, 128GB, tiny, zero), firmware bad detection,
  stack detection
- tests/format.bats: human_bytes (0, KiB, MiB, GiB boundaries, 64GiB),
  human_mib (sub-GiB, exact-GiB, recommended values, empty input)
- tests/benchmark_compare.bats: improvement/regression display, empty
  results, missing files, usage output, config change detection
- tests/log_metrics.bats: CSV header, data format, field count, input
  validation, unknown argument handling
- tests/test_helper.sh: mock sysfs tree builder, bats-assert/support setup

Makefile: add 'make test' target

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_helper.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+# Shared test helper — sets up mocked environment for BATS tests
+
+BATS_SUPPORT="${BATS_SUPPORT:-$HOME/.local/share/bats-support}"
+BATS_ASSERT="${BATS_ASSERT:-$HOME/.local/share/bats-assert}"
+BATS_FILE="${BATS_FILE:-$HOME/.local/share/bats-file}"
+
+load "$BATS_SUPPORT/load.bash"
+load "$BATS_ASSERT/load.bash"
+
+PROJECT_ROOT="$(cd "$(dirname "${BATS_TEST_FILENAME}")/.." && pwd)"
+FIXTURES_DIR="$PROJECT_ROOT/tests/fixtures"
+
+# Create a temporary mock sysfs tree for GPU detection tests
+setup_mock_sysfs() {
+    MOCK_SYSFS="$(mktemp -d)"
+    local gpu_dir="$MOCK_SYSFS/class/drm/card0/device"
+    mkdir -p "$gpu_dir/hwmon/hwmon0"
+
+    echo "0x1002" > "$gpu_dir/vendor"
+    echo "0x1586" > "$gpu_dir/device"
+    echo "${MOCK_VRAM_TOTAL:-536870912}" > "$gpu_dir/mem_info_vram_total"
+    echo "${MOCK_VRAM_USED:-104857600}" > "$gpu_dir/mem_info_vram_used"
+    echo "${MOCK_GTT_TOTAL:-64424509440}" > "$gpu_dir/mem_info_gtt_total"
+    echo "${MOCK_GTT_USED:-209715200}" > "$gpu_dir/mem_info_gtt_used"
+    echo "${MOCK_GPU_BUSY:-5}" > "$gpu_dir/gpu_busy_percent"
+    echo "${MOCK_GPU_TEMP:-50000}" > "$gpu_dir/hwmon/hwmon0/temp1_input"
+    echo "${MOCK_GPU_POWER:-25000000}" > "$gpu_dir/hwmon/hwmon0/power1_average"
+
+    export GPU_SYSFS="$gpu_dir"
+}
+
+teardown_mock_sysfs() {
+    [[ -n "${MOCK_SYSFS:-}" ]] && rm -rf "$MOCK_SYSFS"
+}
+
+# Create a mock /proc/cmdline
+setup_mock_cmdline() {
+    MOCK_PROC="$(mktemp -d)"
+    echo "${MOCK_CMDLINE:-BOOT_IMAGE=/boot/vmlinuz root=UUID=abc ro quiet}" > "$MOCK_PROC/cmdline"
+}
+
+teardown_mock_proc() {
+    [[ -n "${MOCK_PROC:-}" ]] && rm -rf "$MOCK_PROC"
+}
+
+# Source a lib file with PROJECT_ROOT set correctly
+source_lib() {
+    local lib="$1"
+    # Disable color for predictable test output
+    export TERM=dumb
+    source "$PROJECT_ROOT/lib/$lib"
+}