feat: Neon Alley — urban-Japan movement map built on the acoustic materials

New map (scenes/maps/neon_alley/, auto-appears in the level selectors):

Layout for movement flow:
- Main N-S street = the long sightline, crossed by a pedestrian bridge
  (slide ramps up both ends, underpass cover below, railed high ground)
- West machiya row: wooden two-story houses with a jump route
  (awning -> balcony -> roof deck) and 25-degree slide roofs facing the street
- East concrete towers with glass storefronts; brick wallrun alley between
  them (AC units to vault); metal fire-escape platform route to the roofs;
  angled rooftop billboard as cover + grapple anchor
- Three power pylons with crossarms over the street chain a grapple route;
  the torii gate crossbeam at the north shrine plaza is a fourth anchor
- South market: wooden stalls with neon canopies + metal vending machines
  = scattered mid cover; shipping container corner piece
- Spawns ring the block and face the map center

Acoustics as level design: every surface is tagged (machiya/stalls/torii
wood, towers concrete, storefronts glass, alley+perimeter brick, escapes/
AC/rails/container metal) so occlusion tells you which structure a shot
came through and reflections differ per street.

Style: sunset sky + fixed dusk-lavender ambient (calibrated for the toon
shader's 1/PI light response), warm low sun, neon sign columns, shop signs,
lantern strings, billboard glow, underpass strip lights.

Verified: aerial + street-level + third-person captures; movement 11/11,
smoke 0 failures, acoustics ALL PASSED.

Co-Authored-By: Claude Fable 5 <[email protected]>

scenes/maps/neon_alley/neon_alley.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3 uid="uid://bq3nalley7neon"]
+
+[ext_resource type="Script" path="res://scenes/maps/neon_alley/neon_alley_builder.gd" id="1_na"]
+
+[node name="NeonAlley" type="Node3D"]
+script = ExtResource("1_na")