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_clip_v4.luau

@@ -0,0 +1,125 @@
+-- CLIP PROBE v4 -- FULL-WORKSPACE SCOPE. This is the one that finds the
+-- defect the user can see.
+--
+-- WHY v2 AND v3 BOTH RETURNED A FALSE ZERO:
+--   both scoped obstacles to the `Map` folder. The PA buildings are NOT in
+--   Map -- they are Creator-Store models parented directly to Workspace as
+--   siblings: McDonald's (1666 parts), Gas Station 1 (1463), 7 eleven (627),
+--   Restaurant1, Updated Ramen Shop, Fast Food Restaurant, すき家, Parking lot.
+--   The probes literally could not see the things being speared. A passing
+--   positive control did NOT save me: the control proved the metric works,
+--   not that the SCOPE covers the real obstacles.
+--
+-- v4 collects obstacles from the ENTIRE workspace, excluding only the Map
+-- folder's own drivable/infra parts. Reports per-model hit counts so we know
+-- exactly which shop each ramp is driving through.
+
+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
+
+-- collect drivable parts (ramps especially) from Map
+local drive = {}
+for _, d in ipairs(map:GetDescendants()) do
+	if d:IsA("BasePart") and isDrivable(d.Name) then
+		table.insert(drive, d)
+	end
+end
+
+-- collect obstacles: every BasePart in workspace that is NOT inside Map.
+-- These are the imported building models.
+local obst = {}
+local modelOf = {}
+for _, top in ipairs(ws:GetChildren()) do
+	if top ~= map and not top:IsA("Terrain") and not top:IsA("Camera") then
+		if top:IsA("BasePart") then
+			-- loose parts like stray PAPerimeter/PARampKerb: skip, they're infra
+			if not isDrivable(top.Name) and not top.Name:find("Perimeter") and not top.Name:find("Kerb") then
+				table.insert(obst, top)
+				modelOf[top] = top.Name
+			end
+		else
+			for _, d in ipairs(top:GetDescendants()) do
+				if d:IsA("BasePart") then
+					table.insert(obst, d)
+					modelOf[d] = top.Name
+				end
+			end
+		end
+	end
+end
+
+if #obst == 0 then
+	return "SCOPE FAIL: no obstacles found outside Map"
+end
+
+local op = OverlapParams.new()
+op.FilterType = Enum.RaycastFilterType.Include
+op.FilterDescendantsInstances = obst
+op.MaxParts = 20
+
+-- CONTROL+ : a box at a known obstacle's centre must report a hit
+local tgt = obst[math.floor(#obst / 2)]
+local cPos = ws:GetPartBoundsInBox(CFrame.new(tgt.Position), Vector3.new(4, 4, 4), op)
+-- CONTROL- : empty sky must report zero
+local cNeg = ws:GetPartBoundsInBox(CFrame.new(0, 40000, 0), Vector3.new(8, 8, 8), op)
+local trustworthy = #cPos > 0 and #cNeg == 0
+
+local hits = 0
+local byModel, byRamp = {}, {}
+local samples = {}
+for _, p in ipairs(drive) do
+	local probe = p.Size - Vector3.new(1.0, 1.0, 1.0)
+	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 mn = modelOf[h[1]] or h[1].Name
+			byModel[mn] = (byModel[mn] 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, mn)
+				)
+			end
+		end
+	end
+end
+
+local out = {}
+table.insert(
+	out,
+	("CONTROL+=%d CONTROL-=%d -> %s"):format(#cPos, #cNeg, trustworthy and "TRUSTWORTHY" or "BROKEN-IGNORE")
+)
+table.insert(out, ("drivable=%d obstacles(outside Map)=%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)
+	table.insert(out, label .. ": " .. table.concat(l, " | "))
+end
+if hits > 0 then
+	dump(byModel, "MODELS SPEARED")
+	dump(byRamp, "offending ramp groups")
+	for _, s in ipairs(samples) do
+		table.insert(out, "  " .. s)
+	end
+end
+
+return table.concat(out, "\n")