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).

tools/diag_access_clip.luau

@@ -0,0 +1,145 @@
+-- Diagnose the two reported defects:
+--   (1) ramps not accessible in either direction (connectivity)
+--   (2) ramps pass through buildings (clipping)
+-- Uses native GetPartBoundsInBox so this stays fast on ~22k parts.
+local ws = game:GetService("Workspace")
+local map = ws:FindFirstChild("Map")
+if not map then
+	return "NO MAP"
+end
+
+local BUILDING = {
+	Building = true,
+	TokyoTower = true,
+	TowerDeck = true,
+	TowerAntenna = true,
+	ShiodomeTower = true,
+	TowerCrown = true,
+	DietTower = true,
+	RoppongiHills = true,
+	TokyoStation = true,
+	StationDome = true,
+	Skytree = true,
+	GinzaBlock = true,
+	NationalDiet = true,
+	BridgeTower = true,
+	TowerCrossbeam = true,
+	Structure = true,
+	PalaceWall = true,
+}
+
+local ramp, drivable = {}, {}
+for _, d in ipairs(map:GetDescendants()) do
+	if d:IsA("BasePart") then
+		local n = d.Name
+		if n:find("PAEntryRamp") or n:find("PAExitRamp") then
+			table.insert(ramp, d)
+		elseif n:match("^Road_%d+$") or n == "PAFloor" then
+			table.insert(drivable, d)
+		end
+	end
+end
+if #ramp == 0 then
+	return "no ramp parts"
+end
+
+-- ---------- (2) BUILDING CLIP CHECK ----------
+local op = OverlapParams.new()
+op.MaxParts = 40
+local clipHits, clipNames, worst = 0, {}, {}
+for _, r in ipairs(ramp) do
+	local hits = ws:GetPartBoundsInBox(r.CFrame, r.Size, op)
+	for _, h in ipairs(hits) do
+		if h ~= r and BUILDING[h.Name] then
+			clipHits += 1
+			clipNames[h.Name] = (clipNames[h.Name] or 0) + 1
+			if #worst < 5 then
+				table.insert(worst, ("%s@%.0f,%.0f,%.0f"):format(r.Name, r.Position.X, r.Position.Y, r.Position.Z))
+			end
+			break
+		end
+	end
+end
+
+-- CONTROL: same probe against mainline Road_ parts (known-good, should be ~0)
+local ctrlHits, ctrlN = 0, 0
+for i = 1, #drivable, 9 do
+	local d = drivable[i]
+	ctrlN += 1
+	local hits = ws:GetPartBoundsInBox(d.CFrame, d.Size, op)
+	for _, h in ipairs(hits) do
+		if h ~= d and BUILDING[h.Name] then
+			ctrlHits += 1
+			break
+		end
+	end
+end
+
+local cn = {}
+for k, v in pairs(clipNames) do
+	table.insert(cn, k .. "=" .. v)
+end
+
+-- ---------- (1) CONNECTIVITY ----------
+-- Ramp basename groups, then endpoints of each group by trailing index.
+local groups = {}
+for _, r in ipairs(ramp) do
+	local base, idx = r.Name:match("^(.-)_?(%d+)$")
+	base = base or r.Name
+	idx = tonumber(idx) or 0
+	local g = groups[base]
+	if not g then
+		g = { lo = math.huge, hi = -math.huge, loP = nil, hiP = nil, n = 0 }
+		groups[base] = g
+	end
+	g.n += 1
+	if idx < g.lo then
+		g.lo, g.loP = idx, r
+	end
+	if idx > g.hi then
+		g.hi, g.hiP = idx, r
+	end
+end
+
+-- For an endpoint, find nearest drivable surface and report gap + height delta.
+local function nearestDrivable(p)
+	local bd, bp = math.huge, nil
+	for _, d in ipairs(drivable) do
+		local dd = (d.Position - p).Magnitude
+		if dd < bd then
+			bd, bp = dd, d
+		end
+	end
+	return bd, bp
+end
+
+local lines = {}
+for base, g in pairs(groups) do
+	if g.loP and g.hiP then
+		local d1, p1 = nearestDrivable(g.loP.Position)
+		local d2, p2 = nearestDrivable(g.hiP.Position)
+		table.insert(
+			lines,
+			("%s n=%d | START gap=%.0f dY=%.1f to %s | END gap=%.0f dY=%.1f to %s"):format(
+				base,
+				g.n,
+				d1,
+				p1 and (g.loP.Position.Y - p1.Position.Y) or -999,
+				p1 and p1.Name or "nil",
+				d2,
+				p2 and (g.hiP.Position.Y - p2.Position.Y) or -999,
+				p2 and p2.Name or "nil"
+			)
+		)
+	end
+end
+
+return ("CLIP ramp=%d/%d parts hit buildings [%s] samples=[%s] || CONTROL road %d/%d hit\n%s"):format(
+	clipHits,
+	#ramp,
+	table.concat(cn, ", "),
+	table.concat(worst, " ; "),
+	ctrlHits,
+	ctrlN,
+	table.concat(lines, "\n")
+)