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/control_and_connectivity.luau

@@ -16,7 +16,14 @@ for _, d in ipairs(map:GetDescendants()) do
 		if nm:find("PierColumn") or nm:find("PAMast") or nm:find("GirderRib") then
 			table.insert(structural, d)
 		end
-		for _, base in ipairs({ "PAEntryRampTrunk", "PAEntryRampNear", "PAExitRampTrunk", "PAExitRampNear" }) do
+		for _, base in ipairs({
+			"PAEntryRampTrunk",
+			"PAEntryRampCross",
+			"PAEntryRampNear",
+			"PAExitRampTrunk",
+			"PAExitRampCross",
+			"PAExitRampNear",
+		}) do
 			if nm:sub(1, #base + 1) == base .. "_" then
 				runs[base] = runs[base] or {}
 				table.insert(runs[base], d)
@@ -56,7 +63,14 @@ table.insert(out, "structuralParts=" .. #structural)
 local function sortKey(p)
 	return tonumber(p.Name:match("_(%d+)$")) or 0
 end
-for _, base in ipairs({ "PAEntryRampTrunk", "PAEntryRampNear", "PAExitRampTrunk", "PAExitRampNear" }) do
+for _, base in ipairs({
+	"PAEntryRampTrunk",
+	"PAEntryRampCross",
+	"PAEntryRampNear",
+	"PAExitRampTrunk",
+	"PAExitRampCross",
+	"PAExitRampNear",
+}) do
 	local parts = runs[base]
 	if not parts then
 		table.insert(out, base .. ": MISSING")
@@ -73,8 +87,15 @@ for _, base in ipairs({ "PAEntryRampTrunk", "PAEntryRampNear", "PAExitRampTrunk"
 	end
 end
 
--- Trunk -> Near handoff
-for _, pair in ipairs({ { "PAEntryRampTrunk", "PAEntryRampNear" }, { "PAExitRampTrunk", "PAExitRampNear" } }) do
+-- Handoffs along the flyover chain: Trunk -> Cross -> Near. The ramps now
+-- cross OVER the mainline, so `Cross` sits between the spiral and the
+-- descent; checking Trunk->Near directly would report a false gap.
+for _, pair in ipairs({
+	{ "PAEntryRampTrunk", "PAEntryRampCross" },
+	{ "PAEntryRampCross", "PAEntryRampNear" },
+	{ "PAExitRampTrunk", "PAExitRampCross" },
+	{ "PAExitRampCross", "PAExitRampNear" },
+}) do
 	local t, nr = runs[pair[1]], runs[pair[2]]
 	if t and nr then
 		table.sort(t, function(a, b)