refactor(simulation): rename DistrictSkeleton→QuarterSkeleton per D-222 (#950)

D-222 renamed the 512m generation cell from District to Quarter (District
is now a new 2048m tier above it). Align the generation skeleton code to
the canonical vocabulary. Pure naming — no behavior change; all 1296 lib
tests + integration tests pass unchanged.

Renamed (spatial-cell identifiers):
- DistrictSkeleton → QuarterSkeleton, DistrictWorldState → QuarterWorldState
- DistrictId → QuarterId, DistrictContext/DistrictBoundaries → Quarter*
- field district_id → quarter_id, district_type → quarter_type
- BodyWorldState.districts map → .quarters
- generate_skeleton → generate_quarter_skeleton

Deliberately left as-is (these name functional ZONING, not the spatial
tier — orthogonal to D-222): DistrictType, DistrictLayoutMode, the
district_mix module (DistrictMix/compute_district_mix), and the
GenWorkItem::GenerateSkeleton / GenCompletion::SkeletonGenerated variants.

Also aligned the perception "sim tile" → "subtile" vocabulary (D-222:
Subtile = 0.5m) in decisions/perception.md and the generation-cascade code
comments. Historical D-066/D-094/D-201/D-220 decision bodies keep their
existing D-222 amendment notes (not rewritten in place); the public
max_offset_sim_tiles fn name is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/npc/blueprint.rs

@@ -9,7 +9,7 @@
 //! - `NpcBlueprint` — generator output for a single NPC
 //!
 //! Plus `SpikeOutput` as the top-level binary output container.
-//! These are spike-specific and intentionally decoupled from `DistrictSkeleton`.
+//! These are spike-specific and intentionally decoupled from `QuarterSkeleton`.
 //!
 //! ## Content contract
 //!
@@ -547,7 +547,7 @@ pub enum RelationshipValence {
 
 /// Top-level output for the generator spike binary.
 ///
-/// Intentionally decoupled from `DistrictSkeleton` — this is a proof-of-life
+/// Intentionally decoupled from `QuarterSkeleton` — this is a proof-of-life
 /// container, not production architecture.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct SpikeOutput {