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).

reference/ramps/BUILD_SPEC.md

@@ -0,0 +1,64 @@
+# PA Ramp Build Spec — reconciled
+
+Written 2026-08-03 after research + measurement. Supersedes ad-hoc azimuth
+tuning in `MapBuilder.luau`.
+
+## Source conflict — READ THIS FIRST
+
+Two sources disagree, and the disagreement matters:
+
+| | Generic standard (AASHTO/FHWA/JP, via research) | Measured Daikoku (OSM circle fits) |
+|---|---|---|
+| Ramp form | short shallow **parallel slip road** | **loop helix**, 150–220° of turn |
+| Radius | 80–120 m (285–430 studs) | 71–204 m, mean 131 m (**469 studs**) |
+| Arc | 30–45° | 217° (main helix, rms 1.2 = truly circular) |
+
+**Resolution: measured Daikoku wins for THIS build.** The generic spec describes
+a typical roadside PA on a flat ground-level expressway. Daikoku PA is not that
+— it sits at the bottom of a **five-level junction stack** on reclaimed land, so
+its ramps are genuinely helical loops, not slip roads. The satellite plan view
+(`aerial/daikoku_z19.jpg`) shows one large-radius arc sweeping around the lot.
+
+The generic spec is still authoritative for the **merge detail** (below), which
+is not Daikoku-specific.
+
+## Numbers to build to
+
+| Quantity | Value | Source |
+|---|---|---|
+| Scale | 3.571 studs/m (1 stud = 0.28 m) | project |
+| Main entry helix radius | **525 studs** (147 m) | OSM way 32403901, rms 1.2 |
+| Secondary helix radius | **440 studs** (124 m) | OSM way 779045459, rms 0.7 |
+| Tight connector radius | 255 studs (71 m) | OSM way 32355896 |
+| Turn direction | **clockwise (right) — BOTH ramps** | 6 of 8 OSM ways; video 「右、右」 |
+| Divergence at merge | 2–5° (current build: 0.1–0.2°, tangent) | AASHTO/FHWA |
+| Deceleration lane | 150–200 m before gore | AASHTO |
+| Acceleration lane | 200–300 m after gore | AASHTO |
+| Gore apex angle | < 5°, chevron-painted over 30–50 m | AASHTO |
+| Superelevation | 4–8% bank on curves | AASHTO |
+| Deck-to-deck spacing | 36–43 studs/level (10–12 m) | JP standard |
+
+## Hard constraints (checkable in a probe)
+
+1. **Entry and exit ramps must NEVER intersect.** Current build fails this:
+   2547 point-pairs within 30 studs planar at < 12 studs dY, worst case
+   **0.5 studs apart at dY = 0.0**. This is the dominant visual defect —
+   it reads as a bowtie tangle. Probe must assert 0 such pairs.
+2. Both ramps curve **the same direction** (clockwise). They are at opposite
+   ends of the lot and wrap the same way; they do not mirror into each other.
+3. Ramp arc wraps **outside** the parking apron, forming its boundary — it does
+   not cut across the lot interior.
+4. Merge is tangent (already achieved: 0.1–0.2°).
+5. No ramp part intersects any Workspace-level building model (obstacle scope
+   must be INVERTED, not a name whitelist — see verification skill).
+
+## Edge / structure treatment (from onboard video + Commons photos)
+
+- Edge = **low concrete jersey base + see-through chain-link mesh fence above**.
+  NOT a tall solid parapet. Current build's heavy kerb chain is why the ramps
+  read as thick white rails.
+- **Red/orange chevron shoulder paint** through every ramp curve — present in
+  all five reference videos, day and night. Cheapest high-value detail.
+- Piers: **large cylindrical columns**, widely spaced, under a **trapezoidal
+  box-girder** deck underside. White/pale concrete.
+- White zebra hatching fills the gore wedge.