Make the ladder runnable on this fork's rig — 6 of 7 rungs now hold

This fork had never been gated end to end. Five separate things stopped it, none
of them a defect in the CAD code itself, and each failure named the wrong
subsystem — which is why they survived.

1. run-all-checks.sh invoked docs/ux/mockups/gen_offer_table.py. The design docs
   moved to docs/CAD/ (bbd1989e1e) and this path did not follow, so the rung
   failed on a missing file.
2. gen_offer_table.py then resolved REPO one dirname short, because it now sits a
   level deeper. OUT pointed at docs/src/.../DesignOffer.hpp, which does not
   exist, so --check diffed the generated table against an EMPTY file and
   reported all 189 lines as a difference.
3. DISPLAY was never passed into the container. The check scripts fall back to
   ":10", which is the other fork's rig; this one's Xvfb is :11. Symptom:
   "FATAL no app window on :10", which reads like a dead app.
4. Every absolute chrome coordinate was written in the Snapmaker fork's layout.
   This fork keeps mainline's top row (File / save / undo / redo / Calibration
   with the title), so the whole chrome sits 26 px lower. At the unshifted y the
   Design-tab click landed in the toolbar and the app stayed on the Home page,
   reported as "no sketch opened after plane click + Shift+S"; the unshifted
   Construction checkbox reported "0 construction axis". The three constants now
   derive from CHROME_DY. Canvas coordinates were never affected -- clickmm()
   computes them from live canvas geometry -- which is why dozens of geometric
   properties passed exactly on a GUI that had never been driven.
5. CON_BTN was stale for every index after 5, from the sketch epic's six new
   buttons. Fixed in both forks; see the companion commit on snaporca.

pdftocairo was also missing from the rig image (installed there, not a repo
change), without which every corpus sheet threw.

RESULT: offer-table, kernel, engine, corpus, corpus-scale and offer all hold.
The gesture ladder now reaches D2 and applies Equal length through the Constrain
toolbar, both sides landing at 99.928133658; it then fails re-entering the sketch
after commit, filed as snaporca-eoj1 with the evidence and the next measurement
to take. Kernel here is 7701 assertions / 270 cases.

scripts/CAD/run-all-checks.sh

@@ -38,17 +38,26 @@ step() {
 # SC2329: every call goes through step(), which invokes it via "$@", so shellcheck
 # cannot see the callers below.
 # shellcheck disable=SC2329
+# This fork's rig runs Xvfb on :11, the other fork's on :10, and the check scripts default
+# to ":10" when DISPLAY is unset -- which docker exec leaves unset. The rungs that drive the
+# GUI therefore looked for a window on a display that does not exist here and reported
+# "FATAL no app window on :10", which reads like a dead app rather than a wrong display.
+RIG_DISPLAY="${RIG_DISPLAY:-:11}"
+
 run_in_rig() {                      # copy the script in fresh, then run it there
     docker cp "$1" "$C:/tmp/$(basename "$1")" >/dev/null || return 1
     shift
-    docker exec "$C" python3 "$@"
+    docker exec -e DISPLAY="$RIG_DISPLAY" "$C" python3 "$@"
 }
 
 # FIRST, and it needs no rig: the offer table the menu is compiled from must be what the atlas
 # says. The header calls itself GENERATED and had been hand-edited anyway — which cost four rows
 # that existed only in the header, one row wired to the wrong action, and a count of 91 for a
 # 92-row array, so the last verb was unreachable (snaporca-z8rs, snaporca-ziam).
-step "offer table matches the atlas" python3 docs/ux/mockups/gen_offer_table.py --check
+# docs/CAD/, not docs/: SoftFever moved the design docs into the CAD subfolder
+# (bbd1989e1e) and this line kept the old path, so the rung failed on a missing file
+# rather than on anything about the table. The other fork still has docs/ux/.
+step "offer table matches the atlas" python3 docs/CAD/ux/mockups/gen_offer_table.py --check
 
 step "kernel suite" scripts/CAD/run-kernel-tests.sh --vol "${KVOL:-snaporca_kerneltest}"