Aux-lane suppression + PA geometry fixes; probe/verify tooling

MapBuilder.luau
  - Suppress the aux lane across samples 525-550 (AUX_SUPPRESS_FROM/TO),
    honoring the user's hand deletion in Studio so a rebuild no longer
    regenerates it.
  - Smoothstep the width ramp over AUX_BLEND=5 samples on each side. A hard
    cut produced a 26-stud lateral fence jog; the blend removes it.
  - DO NOT remove this suppression. Re-enabling it resurrects geometry the
    user deleted by hand.

rokit.toml
  - rojo 7.5.1 -> 7.7.0 to match the auto-updating Studio plugin.
    Server older than plugin fails the handshake with
    "attempt to index number with 'protocolVersion'".

tools/
  - 34 read-only probe/verify/capture scripts used to measure the datamodel
    instead of reasoning from source.

Verified-good baseline at this commit:
  total parts       16788
  PAWestSlip        60 segs, 34.4 deg total bend, worst 1.4, 0 kinks >5
  PAEastSlip        60 segs, 30.7 deg total bend, worst 1.3, 0 kinks >5
  AuxLane parts     30 (samples 525-550 deliberately absent)
  barrier coverage  823 samples, 0 unguarded
  fence jogs >10st  0

tools/probe_runnable.luau

@@ -0,0 +1,61 @@
+-- Does the game actually RUN? Exercise the real server startup path and report
+-- the first genuine error, rather than guessing from static analysis.
+local RS = game:GetService("ReplicatedStorage")
+local SS = game:GetService("ServerScriptService")
+local out = {}
+local function say(s) table.insert(out, s) end
+
+-- 1. Are the Rojo-synced trees actually present in the DataModel?
+local shared = RS:FindFirstChild("Shared")
+say("ReplicatedStorage.Shared: " .. (shared and "present" or "MISSING"))
+if shared then
+	local names = {}
+	for _, c in ipairs(shared:GetChildren()) do table.insert(names, c.Name) end
+	table.sort(names)
+	say("  modules: " .. table.concat(names, ", "))
+end
+
+local server = SS:FindFirstChild("Server") or SS:FindFirstChild("TS")
+say("ServerScriptService children:")
+for _, c in ipairs(SS:GetChildren()) do
+	say(("  %s (%s)"):format(c.Name, c.ClassName))
+end
+
+-- 2. Try requiring every shared + server module. Report the FIRST failure with
+--    its message -- this is what actually stops a playtest.
+local function tryRequire(inst)
+	local ok, err = pcall(function() return require(inst) end)
+	return ok, err
+end
+
+say("--- require sweep ---")
+local failures = 0
+local tested = 0
+for _, root in ipairs({ shared, server }) do
+	if root then
+		for _, m in ipairs(root:GetDescendants()) do
+			if m:IsA("ModuleScript") then
+				tested += 1
+				local ok, err = tryRequire(m)
+				if not ok then
+					failures += 1
+					say(("FAIL %s: %s"):format(m:GetFullName(), tostring(err):sub(1, 300)))
+				end
+			end
+		end
+	end
+end
+say(("required %d modules, %d failed"):format(tested, failures))
+if tested == 0 then say("CONTROL FAIL: nothing was required -- wrong scope") end
+
+-- 3. Script instances that would run on play, and whether any are disabled.
+say("--- scripts ---")
+for _, d in ipairs(game:GetDescendants()) do
+	if (d:IsA("Script") or d:IsA("LocalScript")) and not d:IsDescendantOf(workspace) then
+		if d.Name:match("init") or d:IsDescendantOf(SS) then
+			say(("  %s (%s) disabled=%s"):format(d:GetFullName(), d.ClassName, tostring(d.Disabled)))
+		end
+	end
+end
+
+return table.concat(out, "\n")