feat(simulation): T-1137 windowed district layer — queue-served, coalesced, determinism-tested (D-226 T-1124 SS1-SS4)

AtlasLayerRequest gains window_center/window_n (serde-default, absent
= whole-body, wire back-compat; demux untouched — up_to stays the
discriminator). DistrictWindowLayer echoes center/n + six parallel
arrays (morphology, elev_q, temp_dc i16 with the region sentinel,
moisture_q, vegetation incl Marine=6, glaciation).

Serving per the amendment's binding model: NEVER inline —
GenWorkItem::DeriveWindow rides the Rayon queue, completion drain
caches into DistrictWindowCache (bounded FIFO 256; no staleness by
D-227 purity, capacity bound only), serve_district_window polls the
cache and returns Pending-shaped None until derived. Per-connection
coalescing: submit_window supersedes a still-pending item for the
same (ConnectionId, body) — the surviving item is the newer one,
proven by dedicated tests.

TerrainAnalysis decision (option b, numbers in ticket/PR): re-derive
via run_layer1 in the DeriveWindow branch rather than caching ~1.5MB
x 50 LRU slots (~100MB permanent, the exact D-203 bloat T-1044's own
text guarded against); ~45ms one-time on the Rayon path, invisible to
the tick thread. T-1044 confirmed within-cascade-only (cascade.rs:358
still drops the analysis before BodyWorldState) — the fork was open.

Window derive loop promoted from aliveness_probe::render_window_panels;
determinism promoted from probe-only proof to a real test (two passes
byte-identical). New fixture atlas_response_ready_with_window
exercises all six arrays incl. the airless sentinel and Marine; three
existing fixtures gain district_window: None. Server clamps window_n
to 1..=DISTRICT_WINDOW_MAX_N=64 (never trust the wire).

1774/1774 lib + 19/19 bridge_tcp green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/tests/fixtures/msgpack/atlas_response_not_found.msgpack

@@ -1 +1 @@
-ˆ§body_id¥ghost¦status¨NotFound¦layer1À­district_gridÀªroad_graphÀ«settlementsÀ«region_gridÀ²quarter_footprintsÀ
+‰§body_id¥ghost¦status¨NotFound¦layer1À­district_gridÀªroad_graphÀ«settlementsÀ«region_gridÀ¯district_windowÀ²quarter_footprintsÀ

client/tests/fixtures/msgpack/atlas_response_pending.msgpack

@@ -1 +1 @@
-êbody_id二J1c存tatus判ending奸ayer1嶺district_grid尷road_graph屨settlements屨region_grid徽quarter_footprints�
+�body_id二J1c存tatus判ending奸ayer1嶺district_grid尷road_graph屨settlements屨region_grid嶸district_window徽quarter_footprints�