Replace coarse lock-key batching with conflict-zone-aware scheduling

Replace string-based conflict keys (source:{nodeId}, target:{nodeId}) with
geometric bounding-box overlap detection. Edges now conflict only when their
routed path bounding boxes overlap spatially (with 40px margin) or share a
repeat-collector label on the same source-target pair.

This enables true spatial parallelism: edges using different sides of the
same node can now be repaired in parallel instead of being serialized.

Sprint 006 TASK-001 final criterion met. All 4 tasks DONE.

Tests verified: StraightExit 2/2, HybridDeterministicMode 3/3,
DocumentProcessingWorkflow artifact 1/1 (all 44+ assertions pass).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/implplan/SPRINT_20260329_006_ElkSharp_hybrid_iterative_routing.md

@@ -24,7 +24,7 @@
 ## Delivery Tracker
 
 ### TASK-001 - Add an opt-in hybrid deterministic iterative routing mode
-Status: DOING
+Status: DONE
 Dependency: none
 Owners: Implementer
 Task description:
@@ -35,7 +35,7 @@ Completion criteria:
 - [x] `IterativeRoutingOptions` exposes `Mode`, `MaxRepairWaves`, and `MaxParallelRepairBuilds`
 - [x] `ElkEdgeRouterIterative.Optimize` can execute a `HybridDeterministic` path without changing legacy behavior by default
 - [x] Hybrid mode preserves fixed Sugiyama node geometry and remains opt-in
-- [ ] Hybrid mode replaces the remaining coarse local-repair lock policy with conflict-zone-aware scheduling across the full repair pipeline
+- [x] Hybrid mode replaces the remaining coarse local-repair lock policy with conflict-zone-aware scheduling across the full repair pipeline
 - [x] Hybrid mode is documented as the recommended path for `LeftToRight` once parity is proven
 
 ### TASK-002 - Add deterministic hybrid parity coverage