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_zsrt139a6_to_board.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+# Ch400: chronological in-bounds base geometry plus bounded alpha tail.
+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 $DATA/sh3_zsrt139a6_epochs.txt"
+k=0
+while [ "$k" -lt 20 ]; do
+    FILES="$FILES $DATA/sh3_zsrt139a6${k}_tex_lpddr.mem $DATA/feeder_sh3_zsrt139a6${k}.mem $DATA/sh3_zsrt139a6${k}_pal.mem"
+    k=$((k + 1))
+done
+for f in $FILES; do [ -f "$f" ] || { echo "MISSING: $f" >&2; exit 1; }; done
+exec scp $FILES "$DEST"