Clean up architecture specs: remove stale references, align docs with code, improve readability

- Replace stale DD references (DD3, DD6, DD9, DD10) with proper ADR links
- Fix 'Open Question 1' → OQ-01/OQ-03 cross-references
- Rewrite metagraph-module.md 'Why TypeBox Modules' to describe capabilities
  directly instead of framing as SchemaBuilder replacement
- Remove 'Transition from SchemaBuilder' section, replace with Source Structure
- Clean up implementation path: strikethrough phases → status table
- Fix data model diagram: remove non-existent nodeTypeId, fix EdgeType label
- Align EdgeConstraints examples with actual code (add default values)
- Clarify validateNode/validateEdge error behavior in docs
- Align EncryptedDataSchema code example with actual implementation
- Fix overview.md: correct dependency table, update current state, fix TypeBox URL
- Fix forward-look.md garbled text about dbtype element migration
- Fix open-questions.md: correct OQ count (4→7 open), add summary table
- Update doc statuses: schema-evolution, encrypted-data, open-questions → reviewed
- Update AGENTS.md to reflect current implementation state

docs/architecture/schema-evolution.md

@@ -1,6 +1,6 @@
 ---
-status: draft
-last_updated: 2026-05-28
+status: reviewed
+last_updated: 2026-05-30
 ---
 
 # Schema Evolution
@@ -504,4 +504,4 @@ questions affecting schema evolution:
 - Event Log as Source of Truth (ADR-005): `/workspace/@alkdev/flowgraph/docs/architecture/decisions/005-event-log-as-source-of-truth.md`
 - Call protocol: `/workspace/@alkdev/operations/docs/architecture/call-protocol.md`
 - Metagraph Module: [metagraph-module.md](./metagraph-module.md)
-- Schema versioning in the data model: [metagraph-module.md](./metagraph-module.md) (Versioning section and DD3)
+- Schema versioning in the data model: ADR-029, [metagraph-module.md](./metagraph-module.md)