Disable PA on/off ramps; restore mainline to pre-ramp state

Three iterations of the Daikoku PA ramps never read as a real
interchange. Measured why, rather than tuning further:

  * the entry and exit decks INTERSECTED -- 2547 sample pairs within
    30 studs horizontally at <12 studs dY, worst case 0.5 studs apart
    at dY=0.0. On screen that is the bowtie tangle of white rails.
  * both real Daikoku ramps turn the SAME way (clockwise; the guide
    video says "right, right"). This build mirrored them into each
    other.
  * the real arc wraps OUTSIDE the lot and forms its north/east
    boundary. This build cut across the apron interior.

Gated behind BUILD_PA_RAMPS=false rather than deleted -- the radius
was already correct (470 studs vs an OSM-measured mean of 469) and
the merge lands tangent at 0.1-0.2 deg divergence. Both worth keeping.

Also removed two leftovers that would have outlived the ramps:

  * rampOpen punched holes in the mainline's outer parapet, railing
    and kill wall for ramps that no longer exist -- a barrier gap with
    a drop behind it. Sealed via RAMP_EDGE_OPENINGS=false. Verified:
    Barrier/EdgeRail/KillWall = 1646 each = 823 samples x 2 edges,
    0 road samples without a guard within 90 studs.
  * gore zebra hatching painted 1024 bars + 64 boundary lines marking
    a junction that is not there. Sealed via RAMP_GORE_MARKINGS=false.

Verified after a cache-busting fresh rebuild (Studio's require() cache
otherwise serves the previous map and reports a false pass):
  parts 22628 -> 15988
  all ramp part classes = 0
  Road = 823 (unchanged), spawn pad + PASpawn intact
  clip probe TRUSTWORTHY (control +11/-0), CLIPPING=0

Research and rebuild spec kept for when this is revisited:
reference/ramps/BUILD_SPEC.md, INDEX.md (10 CC-licensed Commons
photos), docs/daikoku-reference-spec.md (OSM circle fits).

reference/ramps/docs/sat.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""Fetch + stitch Esri World Imagery tiles (no API key) around a lat/lon.
+
+Esri World Imagery over Japan is high-res aerial. Tile scheme is standard
+Web Mercator XYZ, same as OSM.
+"""
+import math, sys, urllib.request, io
+from PIL import Image
+
+URL = "https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}"
+UA = {"User-Agent": "Mozilla/5.0 (X11; Linux x86_64) research/1.0"}
+
+
+def deg2tile(lat, lon, z):
+    lat_r = math.radians(lat)
+    n = 2.0 ** z
+    xt = (lon + 180.0) / 360.0 * n
+    yt = (1.0 - math.asinh(math.tan(lat_r)) / math.pi) / 2.0 * n
+    return xt, yt
+
+
+def fetch(z, x, y):
+    u = URL.format(z=z, x=x, y=y)
+    req = urllib.request.Request(u, headers=UA)
+    with urllib.request.urlopen(req, timeout=30) as r:
+        return Image.open(io.BytesIO(r.read())).convert("RGB")
+
+
+def build(lat, lon, z, half, out):
+    xt, yt = deg2tile(lat, lon, z)
+    cx, cy = int(xt), int(yt)
+    n = half * 2 + 1
+    canvas = Image.new("RGB", (256 * n, 256 * n))
+    ok = 0
+    for i, x in enumerate(range(cx - half, cx + half + 1)):
+        for j, y in enumerate(range(cy - half, cy + half + 1)):
+            try:
+                canvas.paste(fetch(z, x, y), (i * 256, j * 256))
+                ok += 1
+            except Exception as e:
+                print(f"  tile {z}/{x}/{y} FAIL {e}", file=sys.stderr)
+    canvas.save(out, quality=92)
+    # metres per pixel at this latitude
+    mpp = 156543.03392 * math.cos(math.radians(lat)) / (2 ** z)
+    span = mpp * 256 * n
+    print(f"{out}  z={z} tiles={ok}/{n*n} size={canvas.size} "
+          f"mpp={mpp:.3f} span={span:.0f}m")
+    return canvas
+
+
+if __name__ == "__main__":
+    LAT, LON = 35.46246657, 139.68149001
+    build(LAT, LON, 17, 2, "/tmp/daikoku_z17.jpg")   # wide: whole loop
+    build(LAT, LON, 18, 2, "/tmp/daikoku_z18.jpg")   # closer
+    build(LAT, LON, 19, 2, "/tmp/daikoku_z19.jpg")   # detail: stalls