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/verify_source.luau

@@ -0,0 +1,92 @@
+--[[
+	verify_source.luau -- read the module SOURCE TEXT in Edit, bypassing require().
+
+	Why: require() caches a ModuleScript's return value for the whole Studio
+	session. Both modules were pushed successfully (match=true), but an earlier
+	require() in this same session means require() still hands back the OLD
+	table -- so a harness that builds cars via require() measures stale code and
+	can report a false PASS. Reading .Source is cache-proof.
+
+	This only proves the SOURCE is correct on disk-in-Studio. It cannot prove
+	runtime behaviour -- that needs a fresh datamodel (press Play), which
+	rebuilds the require cache from this source.
+]]
+
+local SSS = game:GetService("ServerScriptService")
+local RS = 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
+
+local function find(name: string): ModuleScript?
+	for _, root in ipairs({ SSS, RS }) do
+		local hit = root:FindFirstChild(name, true)
+		if hit and hit:IsA("ModuleScript") then
+			return hit
+		end
+	end
+	return nil
+end
+
+local checks = {
+	{
+		module = "CarManager",
+		label = "isFront convention",
+		want = "local isFront = zSign > 0",
+		bad = "local isFront = zSign < 0",
+	},
+	{
+		module = "CarManager",
+		label = "shell nose solver",
+		want = "shellYaw = -math.atan2(-nose.X, nose.Z)",
+		bad = "shellYaw = -math.atan2(nose.X, -nose.Z)",
+	},
+	{
+		module = "CarManager",
+		label = "SHELL_YAW_OVERRIDE removed",
+		want = nil,
+		bad = "local SHELL_YAW_OVERRIDE",
+	},
+	{
+		module = "Chassis",
+		label = "DRIVE_SIGN",
+		want = "Chassis.DRIVE_SIGN = 1",
+		bad = "Chassis.DRIVE_SIGN = -1",
+	},
+}
+
+local allGood = true
+for _, c in ipairs(checks) do
+	local m = find(c.module)
+	if not m then
+		log(string.format("%-28s MODULE NOT FOUND (%s)", c.label, c.module))
+		allGood = false
+		continue
+	end
+	local src = m.Source
+	local hasWant = (c.want == nil) or (string.find(src, c.want, 1, true) ~= nil)
+	local hasBad = (c.bad ~= nil) and (string.find(src, c.bad, 1, true) ~= nil)
+	local ok = hasWant and not hasBad
+	if not ok then
+		allGood = false
+	end
+	log(string.format("%-28s %-6s  [%s: %d bytes]", c.label, ok and "OK" or "STALE", m:GetFullName(), #src))
+end
+
+log("")
+log(
+	allGood and ">>> SOURCE IS CORRECT in Edit. require() is still caching the old"
+		or ">>> SOURCE IS STALE -- the push did not land."
+)
+if allGood then
+	log("    copies this session, so only a FRESH Play session can prove runtime")
+	log("    behaviour. Save (Ctrl+S), then press Play.")
+end
+
+return table.concat(out, "\n")