Daikoku PA: lift mainline over the apron, rebuild both ramps

The PA ring road and the expressway mainline were both at ground level, so
the ring parapet stood INSIDE the carriageway (measured -10.0 studs of
vertical overlap: a wall in the middle of the road).

Reference photos of the real Daikoku Futo PA show the expressway flying
OVER the parking apron on pillars, with the PA at ground level and ramps
climbing up to meet it. Rebuilt to match:

- mainline lifted 38 studs through the junction, eased in/out (max 5.26%
  grade, within real expressway limits)
- PA ring + apron stay at ground level; legacy PARingPillar props removed
- both on/off ramps regraded over the full rise with smoothstep easing,
  segments overlapped 3 studs so wheels can't catch a seam, plus support
  pillars and edge kerbs where the deck is high

Verified in-engine against built parts (tools/diag_daikoku.luau), not just
source: clearance now +28.0 studs, both ramps continuous (max step 5.62,
no gaps). tools/plot_daikoku.py renders the plan/section for comparison.

tools/fix_dupes.luau

@@ -0,0 +1,92 @@
+--[[
+	fix_dupes.luau -- remove leftover CarManager clones and report the truth.
+
+	diag_stale found TWO ModuleScripts at ServerScriptService.Server.CarManager,
+	both len=30631 with no _buildForDiag, while the file on disk is 39591 bytes
+	and defines it. My diagnostic scripts cloned the module and did not always
+	destroy the clone, so duplicates accumulated; require() may bind to either.
+
+	Deletes every CarManager except the one that is a genuine child of the
+	Server folder (keeping the first by index), then reports what remains so
+	the next push has a single unambiguous target.
+]]
+
+local ServerScriptService = game:GetService("ServerScriptService")
+
+local out = {}
+local function log(...)
+	local parts = {}
+	for i = 1, select("#", ...) do
+		parts[#parts + 1] = tostring((select(i, ...)))
+	end
+	table.insert(out, table.concat(parts, " "))
+end
+
+local server = ServerScriptService:FindFirstChild("Server", true)
+if not server then
+	return "no Server folder"
+end
+
+local mods = {}
+for _, d in ipairs(ServerScriptService:GetDescendants()) do
+	if d:IsA("ModuleScript") and d.Name == "CarManager" then
+		mods[#mods + 1] = d
+	end
+end
+
+log(string.format("found %d CarManager module(s)", #mods))
+for i, m in ipairs(mods) do
+	local len = "?"
+	pcall(function()
+		len = tostring(#m.Source)
+	end)
+	log(
+		string.format(
+			"  [%d] %s  len=%s  parent=%s",
+			i,
+			m:GetFullName(),
+			len,
+			m.Parent and m.Parent:GetFullName() or "nil"
+		)
+	)
+end
+
+-- Keep exactly one: prefer a direct child of the Server folder.
+local keep = nil
+for _, m in ipairs(mods) do
+	if m.Parent == server then
+		keep = m
+		break
+	end
+end
+keep = keep or mods[1]
+
+local removed = 0
+for _, m in ipairs(mods) do
+	if m ~= keep then
+		m:Destroy()
+		removed += 1
+	end
+end
+
+log("")
+log(string.format("kept:    %s", keep and keep:GetFullName() or "nil"))
+log(string.format("removed: %d duplicate(s)", removed))
+
+-- Confirm the survivor
+local after = 0
+for _, d in ipairs(ServerScriptService:GetDescendants()) do
+	if d:IsA("ModuleScript") and d.Name == "CarManager" then
+		after += 1
+	end
+end
+log(string.format("remaining CarManager count: %d", after))
+if keep then
+	local len = "?"
+	pcall(function()
+		len = tostring(#keep.Source)
+	end)
+	log("survivor source length: " .. len .. "  (disk file is 39591)")
+end
+
+return table.concat(out, "\n")