Snapshot: fog implementation + fidelity tooling baseline (pre bilinear-clamp fix)

Per-vertex GS fog end-to-end (gs_stub emit incl. persp_emit5, gs_prim_list_feeder
XYZ2->XYZF2 on PRIM.FGE, gs_make_sh3_scheduler_fixture.py F/FGE packing), new fog
TBs, fidelity attribution tooling. Functional baseline before removing the dead
bilinear lerp8 clamps (Codex: 161-node comb loop -> -0.042ns setup fail).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/scp_zs640c18_to_board.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+# Copy Ch361 C18 host data only. Its bootlet words are byte-identical to the loaded C6 core; no RBF is copied.
+set -eu
+
+DEST="${1:-terasic@192.168.50.161:~}"
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+DATA="$ROOT/sim/data/top_psmct32_raster_demo"
+FILES="
+$ROOT/tools/ps2_sh3_sched.c
+$DATA/sh3_zs640c18_epochs.txt
+$DATA/sh3_zs640c180_tex_lpddr.mem
+$DATA/feeder_sh3_zs640c180.mem
+$DATA/feeder_sh3_zs640c181.mem
+$DATA/feeder_sh3_zs640c182.mem
+$DATA/feeder_sh3_zs640c183.mem
+$DATA/feeder_sh3_zs640c184.mem
+$DATA/feeder_sh3_zs640c185.mem
+"
+
+missing=0
+for f in $FILES; do
+    if [ ! -f "$f" ]; then echo "MISSING: $f" >&2; missing=1; fi
+done
+if [ "$missing" -ne 0 ]; then
+    echo "Regenerate C18 first: make -C sim sh3_zs640c18_fixture" >&2
+    exit 1
+fi
+
+echo "Copying 9 C18 host/data files -> $DEST"
+# shellcheck disable=SC2086
+exec scp $FILES "$DEST"