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>

iso/overlay/usr/local/bin/bee-hpl

@@ -0,0 +1,97 @@
+#!/bin/sh
+# bee-hpl — run HPL (High Performance LINPACK) with auto-sized problem.
+#
+# Generates HPL.dat based on available RAM, runs xhpl, and prints standard
+# HPL output. The WR... line with Gflops is parsed by the bee audit tool.
+#
+# Usage: bee-hpl [--mem-fraction 0.80] [--nb 256] [--seconds N]
+#
+# --mem-fraction   fraction of total RAM to use for the matrix (default 0.80)
+# --nb             block size; 256 is good for modern CPUs (default 256)
+# --seconds        ignored — HPL runtime is determined by problem size; kept
+#                  for interface compatibility with other bee stress tools
+
+set -eu
+
+XHPL="/usr/local/lib/bee/xhpl"
+MEM_FRACTION="0.80"
+NB=256
+
+usage() {
+    echo "usage: $0 [--mem-fraction 0.80] [--nb 256] [--seconds N]" >&2
+    exit 2
+}
+
+while [ "$#" -gt 0 ]; do
+    case "$1" in
+        --mem-fraction) [ "$#" -ge 2 ] || usage; MEM_FRACTION="$2"; shift 2 ;;
+        --nb)           [ "$#" -ge 2 ] || usage; NB="$2"; shift 2 ;;
+        --seconds)      [ "$#" -ge 2 ] || usage; shift 2 ;;  # accepted, ignored
+        *) usage ;;
+    esac
+done
+
+[ -x "${XHPL}" ] || { echo "ERROR: xhpl not found at ${XHPL}" >&2; exit 1; }
+
+# Detect total RAM in bytes
+TOTAL_KB=$(grep MemTotal /proc/meminfo | awk '{print $2}')
+[ -n "${TOTAL_KB}" ] || { echo "ERROR: cannot read MemTotal from /proc/meminfo" >&2; exit 1; }
+TOTAL_BYTES=$(( TOTAL_KB * 1024 ))
+
+# N = floor(sqrt(fraction * total_bytes / 8)) rounded down to multiple of NB
+# Use awk for floating-point sqrt
+N=$(awk -v total="${TOTAL_BYTES}" -v frac="${MEM_FRACTION}" -v nb="${NB}" '
+BEGIN {
+    raw = int(sqrt(total * frac / 8.0))
+    n   = int(raw / nb) * nb
+    if (n < nb) n = nb
+    print n
+}')
+
+echo "loader=bee-hpl"
+echo "total_ram_mb=$(( TOTAL_KB / 1024 ))"
+echo "matrix_n=${N}"
+echo "block_nb=${NB}"
+echo "mem_fraction=${MEM_FRACTION}"
+
+# Generate HPL.dat in a temp directory and run from there
+RUNDIR=$(mktemp -d)
+trap 'rm -rf "${RUNDIR}"' EXIT INT TERM
+
+cat > "${RUNDIR}/HPL.dat" <<DAT
+HPLinpack benchmark input file
+Innovative Computing Laboratory, University of Tennessee
+HPL.out        output file name (if any)
+6              device out (6=stdout, 7=stderr, file)
+1              # of problems sizes (N)
+${N}           Ns
+1              # of NBs
+${NB}          NBs
+0              PMAP process mapping (0=Row-,1=Column-major)
+1              # of process grids (P x Q)
+1              Ps
+1              Qs
+16.0           threshold
+1              # of panel fact
+2              PFACTs (0=left, 1=Crout, 2=Right)
+1              # of recursive stopping criterium
+4              NBMINs (>= 1)
+1              # of panels in recursion
+2              NDIVs
+1              # of recursive panel fact.
+1              RFACTs (0=left, 1=Crout, 2=Right)
+1              # of broadcast
+1              BCASTs (0=1rg,1=1rM,2=2rg,3=2rM,4=Lng,5=LnM)
+1              # of lookahead depth
+1              DEPTHs (>=0)
+2              SWAP (0=bin-exch,1=long,2=mix)
+64             swapping threshold
+0              L1 in (0=transposed,1=no-transposed) form
+0              U  in (0=transposed,1=no-transposed) form
+1              Equilibration (0=no,1=yes)
+8              memory alignment in double (> 0)
+DAT
+
+cd "${RUNDIR}"
+echo "---"
+"${XHPL}"