feat: add isometric graph visualization stack for Slint UI

- Add graph.rs: NodeData, EdgeData, pipeline node/edge vectors
- Add layout.rs: ForceLayout with custom Fruchterman-Reingold solver, iso_project()
- Add render.rs: GraphRenderer for screen coordinate mapping
- Add slint_viz.rs: SlintGraphView with Arc<RwLock<ForceLayout>>
- Add visualize.rs: Mermaid generation, HTML export, Kasuari layout solver
- Add validation.rs: Disposition, MetaCtx, VerbDef, StageResult
- Add legal.rs: Jurisdiction (US/AU/UK), LegalSolver
- Add constraints.rs: VendorConstraintSet, Kasuari strengths
- Add verify.rs: Multi-model proposer/reviewer
- Add workflow.rs: TOML DSL compiler → Mermaid/Rhai/Rust
- Add pipeline.rs: Type-state pipeline with statig HSM
- Add E2E visualization tests

Implements 6-layer architecture:
- Layer 0: petgraph data model (simplified to vectors)
- Layer 1: force-directed layout
- Layer 2: isometric projection
- Layer 3: femtovg renderer (screen coords)
- Layer 4: Slint texture bridge
- Layer 5: Slint UI component

Author: Claude Sonnet (coordinator)

.planning/research/TYPE_SYSTEM_PATTERNS.md

@@ -300,6 +300,15 @@ Treat this as a standing operational gate, not a one-time migration task.
   - Persist ingest idempotency state, transaction row cache, audit log, lifecycle event history, and HSM checkpoint together as one snapshot.
   - Keep the workbook as the human/accountant artifact; do not overload it as the only machine recovery mechanism for agent queues and replay state.
   - If the sidecar exists but cannot be parsed or its version is unsupported, fail closed instead of silently resetting state.
+- 2026-04-19: P1 validation framework adds verb-centric pipeline with carry-forward confidence model.
+  - Disposition (Unrecoverable/Recoverable/Advisory) on every Issue for clear signal on what action to take.
+  - MetaCtx.accumulated_confidence compounds multiplicatively across stages.
+  - LegalSolver verifies transactions against tax rules (AU GST Act s38-190, US Schedule C).
+  - VendorConstraintSet evaluates data plausibility using Kasuari strengths.
+  - WorkflowToml is single source of truth — compiles to Mermaid diagram for operator and Rhai FSM for execution.
+  - VerbDef captures reversibility and access criteria (Commit/Reverse require Tray approval).
+  - Multi-model verification loop: LLM proposes, second model reviews, operator approves.
+  - Multi-jurisdiction: US/AU/UK with rules keyed by Jurisdiction.