Add HPL (LINPACK) benchmark as validate/stress task

HPL 2.3 from netlib compiled against OpenBLAS with a minimal
single-process MPI stub — no MPI package required in the ISO.
Matrix size is auto-sized to 80% of total RAM at runtime.

Build:
- VERSIONS: HPL_VERSION=2.3, HPL_SHA256=32c5c17d…
- build-hpl.sh: downloads HPL + OpenBLAS from Debian 12 repo,
  compiles xhpl with a self-contained mpi_stub.c
- build.sh: step 80-hpl, injects xhpl + libopenblas into overlay

Runtime:
- bee-hpl: generates HPL.dat (N auto from /proc/meminfo, NB=256,
  P=1 Q=1), runs xhpl, prints standard WR... Gflops output
- platform/hpl.go: RunHPL(), parses WR line → GFlops + PASSED/FAILED
- tasks.go: target "hpl"
- pages.go: LINPACK (HPL) card in validate/stress grid (stress-only)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/app/app.go

@@ -139,6 +139,7 @@ type satRunner interface {
 	RunFanStressTest(ctx context.Context, baseDir string, opts platform.FanStressOptions) (string, error)
 	RunPlatformStress(ctx context.Context, baseDir string, opts platform.PlatformStressOptions, logFunc func(string)) (string, error)
 	RunNCCLTests(ctx context.Context, baseDir string, logFunc func(string)) (string, error)
+	RunHPL(ctx context.Context, baseDir string, opts platform.HPLOptions, logFunc func(string)) (string, *platform.HPLResult, error)
 }
 
 type runtimeChecker interface {
@@ -737,6 +738,13 @@ func (a *App) RunNCCLTestsResult(ctx context.Context) (ActionResult, error) {
 	return ActionResult{Title: "NCCL bandwidth test", Body: body}, err
 }
 
+func (a *App) RunHPL(ctx context.Context, baseDir string, opts platform.HPLOptions, logFunc func(string)) (string, *platform.HPLResult, error) {
+	if a == nil {
+		return "", nil, fmt.Errorf("app not configured")
+	}
+	return a.sat.RunHPL(ctx, baseDir, opts, logFunc)
+}
+
 func (a *App) RunFanStressTestResult(ctx context.Context, opts platform.FanStressOptions) (ActionResult, error) {
 	path, err := a.RunFanStressTest(ctx, "", opts)
 	body := formatFanStressResult(path)