feat(simulation): road-graph hub refinement — scaled-cap hubs, co-location collapse, minor-attach edge split, RailHeadFacing (T-1076)

is_standalone_hq threaded through CityRecord/CityPlacement via corporations LEFT JOIN (both readers); hubs = top-cap by population among non-HQ settlements (HUB_SPACING_DIAG_PX=64, HUB_CAP_MIN=6); exact-name collapse keeping lowest city_id with loud warn; nearest-point-on-polyline snap (SNAP_MAX_PX=8) with Junction edge-split preserving from<to via norm_edge, else A*-spur to nearest hub; FoundingOrientation::RailHeadFacing{bearing_degrees} assigned at degree>=3 junctions (octant bearing toward dominant incident edge), consumed by skeleton_gen railhead_edge() through the D-234b flush-frontage machinery; believability reader now honours baked settlement_class (stale hardcode since T-1075). 11 new targeted tests; existing suites green.

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

server/src/simulation/generator.rs

@@ -410,6 +410,16 @@ pub enum FoundingOrientation {
     Cardinal,
     /// Arbitrary bearing (pioneer settlements on open terrain). `bearing_degrees`: 0–359.
     Free { bearing_degrees: u16 },
+    /// Street grid faces the settlement's rail head (D-213 amended, T-1076 §4).
+    /// Assigned POST-placement by the Layer-2 road-graph pass
+    /// (`road_graph::assign_railhead_orientations`) — never by the attractor
+    /// match — to settlements that are high-connectivity junctions
+    /// (`RoadGraph::high_connectivity_junctions`, degree ≥ 3, per the D-213
+    /// workshop source paula-round3.md). `bearing_degrees`: octant-snapped
+    /// compass bearing (0–359, 0 = N, clockwise; integer octants only, D-010)
+    /// from the settlement toward the dominant (longest) incident road/rail
+    /// edge — the direction the freight frontage faces.
+    RailHeadFacing { bearing_degrees: u16 },
 }
 
 /// Who maintains an inter-settlement road/rail edge — readable in the road's