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/probe_building_clip_v3.luau

@@ -0,0 +1,146 @@
+-- CLIP PROBE v3 -- INVERTED SCOPE.
+--
+-- v2 tested drivable parts against a HARDCODED WHITELIST of 16 building
+-- names (Building, TokyoTower, GinzaBlock, ...). It reported CLIPPING=0 with
+-- a passing control, and I reported that as fact. The user can see ramps
+-- going through buildings, so the zero was false.
+--
+-- The bug is the whitelist: any obstacle whose name isn't one of those 16 is
+-- invisible to the test. The PA structures (shops, kiosks, canopies) are the
+-- prime suspect -- they sit exactly where the ramp ends land.
+--
+-- v3 inverts the scope: an obstacle is ANY part that is not drivable and not
+-- infrastructure (pier/rail/sign/ground). No name list to go stale.
+-- It also reports offenders GROUPED BY OBSTACLE NAME, so the answer names
+-- the thing being speared instead of just counting.
+
+local ws = game:GetService("Workspace")
+local map = ws:FindFirstChild("Map")
+if not map then
+	return "NO MAP"
+end
+
+local function isDrivable(n)
+	return n:match("^Road_")
+		or n:find("Ramp")
+		or n == "PAFloor"
+		or n:match("^Apron")
+		or n:match("^Slip")
+		or n:match("^Merge")
+end
+
+-- things that are ALLOWED to intersect a road (structure, decor, markings)
+local function isInfra(n)
+	return n:find("Pier")
+		or n:find("Pillar")
+		or n:find("Column")
+		or n:find("Support")
+		or n:find("Beam")
+		or n:find("Rail")
+		or n:find("Guard")
+		or n:find("Barrier")
+		or n:find("Sign")
+		or n:find("Light")
+		or n:find("Lamp")
+		or n:find("Line")
+		or n:find("Mark")
+		or n:find("Stripe")
+		or n:find("Deck")
+		or n:find("Water")
+		or n == "Ground"
+		or n:find("Grounds")
+		or n:find("Median")
+		or n:find("Curb")
+		or n:find("Wall")
+end
+
+local drive, obst = {}, {}
+for _, d in ipairs(map:GetDescendants()) do
+	if d:IsA("BasePart") then
+		local n = d.Name
+		if isDrivable(n) then
+			table.insert(drive, d)
+		elseif not isInfra(n) then
+			table.insert(obst, d)
+		end
+	end
+end
+
+if #obst == 0 or #drive == 0 then
+	return ("SCOPE FAIL drive=%d obst=%d"):format(#drive, #obst)
+end
+
+local op = OverlapParams.new()
+op.FilterType = Enum.RaycastFilterType.Include
+op.FilterDescendantsInstances = obst
+op.MaxParts = 12
+
+-- POSITIVE CONTROL: probe dead-centre of a known obstacle must report a hit.
+local target = obst[math.floor(#obst / 2)]
+local ctrl = ws:GetPartBoundsInBox(CFrame.new(target.Position), Vector3.new(4, 4, 4), op)
+local controlOK = #ctrl > 0
+
+-- SECOND CONTROL: a box far out in empty sky must report ZERO. Guards the
+-- opposite failure -- a filter so broad everything "hits".
+local negCtrl = ws:GetPartBoundsInBox(CFrame.new(0, 40000, 0), Vector3.new(8, 8, 8), op)
+local negOK = #negCtrl == 0
+
+local hits = 0
+local byObst, byRamp = {}, {}
+local samples = {}
+for _, p in ipairs(drive) do
+	local probe = p.Size - Vector3.new(1.5, 1.5, 1.5)
+	if probe.X > 0.5 and probe.Y > 0.5 and probe.Z > 0.5 then
+		local h = ws:GetPartBoundsInBox(p.CFrame, probe, op)
+		if #h > 0 then
+			hits += 1
+			local on = h[1].Name
+			byObst[on] = (byObst[on] or 0) + 1
+			local rn = p.Name:gsub("_%d+$", "")
+			byRamp[rn] = (byRamp[rn] or 0) + 1
+			if #samples < 10 then
+				table.insert(
+					samples,
+					("%s@%.0f,%.0f,%.0f IN %s"):format(p.Name, p.Position.X, p.Position.Y, p.Position.Z, on)
+				)
+			end
+		end
+	end
+end
+
+local out = {}
+table.insert(
+	out,
+	("CONTROL+=%s(%d)  CONTROL-=%s(%d)  -> probe %s"):format(
+		controlOK and "PASS" or "FAIL",
+		#ctrl,
+		negOK and "PASS" or "FAIL",
+		#negCtrl,
+		(controlOK and negOK) and "TRUSTWORTHY" or "BROKEN-IGNORE-RESULTS"
+	)
+)
+table.insert(out, ("drivable=%d obstacles=%d CLIPPING=%d"):format(#drive, #obst, hits))
+
+local function dump(t, label)
+	local l = {}
+	for k, v in pairs(t) do
+		table.insert(l, ("%s=%d"):format(k, v))
+	end
+	table.sort(l, function(a, b)
+		return a > b
+	end)
+	local keep = {}
+	for i = 1, math.min(#l, 12) do
+		table.insert(keep, l[i])
+	end
+	table.insert(out, label .. ": " .. table.concat(keep, " "))
+end
+if hits > 0 then
+	dump(byObst, "speared obstacles")
+	dump(byRamp, "offending road groups")
+	for _, s in ipairs(samples) do
+		table.insert(out, "  " .. s)
+	end
+end
+
+return table.concat(out, "\n")