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/route.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python3
+"""Download a route video, sample frames every N seconds, and build labelled
+contact sheets. Built for Daikoku entrance/exit reference gathering.
+
+Usage: route.py <videoid> <shortname> [step_seconds]
+"""
+import os, re, subprocess, sys, glob, json
+from PIL import Image, ImageDraw
+
+YTDLP = os.path.expanduser("~/.local/bin/yt-dlp")
+ROOT = "/tmp/routes"
+
+
+def run(cmd, **kw):
+    return subprocess.run(cmd, shell=True, capture_output=True, text=True, **kw)
+
+
+def meta(vid):
+    r = run(f'{YTDLP} --no-warnings -J --skip-download "https://www.youtube.com/watch?v={vid}" 2>/dev/null')
+    try:
+        d = json.loads(r.stdout)
+    except Exception:
+        return {}
+    return {k: d.get(k) for k in ("title", "uploader", "duration", "upload_date", "width", "height")}
+
+
+def fetch(vid, name):
+    d = f"{ROOT}/{name}"
+    os.makedirs(d, exist_ok=True)
+    mp4 = f"{d}/{name}.mp4"
+    if not os.path.exists(mp4):
+        r = run(f'{YTDLP} -f "bv*[height<=1080][ext=mp4]/bv*[height<=1080]/b" '
+                f'--no-warnings -o "{mp4}" "https://www.youtube.com/watch?v={vid}"')
+        if not os.path.exists(mp4):
+            print(f"  DOWNLOAD FAILED: {r.stderr[-300:]}")
+            return None
+    return mp4
+
+
+def sample(mp4, d, step):
+    dur = float(run(f'ffprobe -v error -show_entries format=duration '
+                    f'-of default=nw=1:nk=1 "{mp4}"').stdout.strip() or 0)
+    for f in glob.glob(f"{d}/fr_*.jpg"):
+        os.remove(f)
+    ts = list(range(2, int(dur), step))
+    for t in ts:
+        run(f'ffmpeg -v error -ss {t} -i "{mp4}" -frames:v 1 -q:v 2 '
+            f'-vf scale=960:-1 "{d}/fr_{t:04d}.jpg" -y')
+    return dur, ts
+
+
+def sheets(d, name, cols=3, per=9):
+    fs = sorted(glob.glob(f"{d}/fr_*.jpg"))
+    out = []
+    for page in range((len(fs) + per - 1) // per):
+        sub = fs[page * per:(page + 1) * per]
+        ims = [Image.open(f).convert("RGB") for f in sub]
+        w, h = ims[0].size
+        rows = (len(sub) + cols - 1) // cols
+        s = Image.new("RGB", (w * cols, h * rows), (10, 10, 10))
+        for i, im in enumerate(ims):
+            s.paste(im, ((i % cols) * w, (i // cols) * h))
+        dr = ImageDraw.Draw(s)
+        for i, f in enumerate(sub):
+            t = int(re.search(r"fr_(\d+)", f).group(1))
+            x, y = (i % cols) * w, (i // cols) * h
+            dr.rectangle([x + 6, y + 6, x + 190, y + 54], fill=(0, 0, 0))
+            dr.text((x + 20, y + 22), f"t={t}s", fill=(255, 225, 0))
+        s = s.resize((int(s.width * 0.60), int(s.height * 0.60)), Image.LANCZOS)
+        o = f"{d}/{name}_sheet{page+1}.jpg"
+        s.save(o, quality=90)
+        out.append(o)
+    return out
+
+
+if __name__ == "__main__":
+    vid, name = sys.argv[1], sys.argv[2]
+    step = int(sys.argv[3]) if len(sys.argv) > 3 else 8
+    m = meta(vid)
+    print(f"=== {name} [{vid}] ===")
+    print(f"  title: {m.get('title')}")
+    print(f"  dur  : {m.get('duration')}s  {m.get('width')}x{m.get('height')}")
+    mp4 = fetch(vid, name)
+    if not mp4:
+        sys.exit(1)
+    d = f"{ROOT}/{name}"
+    dur, ts = sample(mp4, d, step)
+    sh = sheets(d, name)
+    print(f"  frames: {len(ts)} @ {step}s  sheets: {len(sh)}")
+    for s in sh:
+        print(f"   {s}")