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/diag_stale.luau

@@ -0,0 +1,101 @@
+--[[
+	diag_stale.luau -- is the live CarManager module the source I pushed?
+
+	diag_wheelroot2 failed with "_buildForDiag is nil" even though the file on
+	disk defines it at line 988 and push_module reported
+	assembled=39591 expected=39591 match=true.
+
+	So either (a) the ModuleScript I am cloning is not the one I pushed to, or
+	(b) there is more than one CarManager, or (c) the clone-and-require trick
+	is returning a cached table from the ORIGINAL require rather than
+	re-executing the clone's source.
+
+	(c) is the important one: if require(clone) hands back the cached original
+	table, then every "built car" measurement in this session came from the
+	OLD module, and all of those results are void.
+
+	Checks, with no assumptions:
+	  1. Every ModuleScript named CarManager anywhere in the DataModel, with
+	     its source length and whether its text contains _buildForDiag.
+	  2. What require() actually returns for the original and for a fresh
+	     clone -- key list and identity comparison.
+]]
+
+local ServerScriptService = game:GetService("ServerScriptService")
+local ReplicatedStorage = game:GetService("ReplicatedStorage")
+
+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
+
+log("=== every CarManager ModuleScript in the DataModel ===")
+local found = {}
+for _, svc in ipairs({ ServerScriptService, ReplicatedStorage, game:GetService("ServerStorage"), workspace }) do
+	for _, d in ipairs(svc:GetDescendants()) do
+		if d:IsA("ModuleScript") and d.Name == "CarManager" then
+			found[#found + 1] = d
+			local src = ""
+			local okSrc = pcall(function()
+				src = d.Source
+			end)
+			log(
+				string.format(
+					"  %-58s len=%s  has _buildForDiag=%s",
+					d:GetFullName(),
+					okSrc and tostring(#src) or "<unreadable>",
+					okSrc and tostring(src:find("_buildForDiag") ~= nil) or "?"
+				)
+			)
+		end
+	end
+end
+log(string.format("  total found: %d", #found))
+
+if #found == 0 then
+	return table.concat(out, "\n")
+end
+
+local target = found[1]
+
+log("")
+log("=== what require() returns ===")
+local okA, A = pcall(require, target)
+log("  require(original): ok=" .. tostring(okA))
+if okA and typeof(A) == "table" then
+	local keys = {}
+	for k in pairs(A) do
+		keys[#keys + 1] = tostring(k)
+	end
+	table.sort(keys)
+	log("    keys: " .. table.concat(keys, ", "))
+	log("    _buildForDiag = " .. typeof(A._buildForDiag))
+end
+
+local clone = target:Clone()
+clone.Parent = target.Parent
+local okB, B = pcall(require, clone)
+log("  require(clone):    ok=" .. tostring(okB))
+if okB and typeof(B) == "table" then
+	local keys = {}
+	for k in pairs(B) do
+		keys[#keys + 1] = tostring(k)
+	end
+	table.sort(keys)
+	log("    keys: " .. table.concat(keys, ", "))
+	log("    _buildForDiag = " .. typeof(B._buildForDiag))
+end
+if okA and okB then
+	log(
+		"  clone table IS original table: "
+			.. tostring(rawequal(A, B))
+			.. "   <- if true, the clone trick does NOT reload source"
+	)
+end
+clone:Destroy()
+
+return table.concat(out, "\n")