docs: add module documentation in AsciiDoc with PlantUML diagrams

Generated by per-group subagents covering all 52 modules across:
core (18), infrastructure (10), apps (5), interfaces (3),
plugins (7), testing (9)

Documentation format:
- AsciiDoc (.adoc) files in docs/modules/<group>/
- PlantUML (.puml) files in docs/diagrams/
- .adoc files reference diagrams via include:: directives

Each doc covers: purpose, responsibilities, non-responsibilities,
key types, event flow, integration points, invariants, PlantUML
diagram, known issues, and open questions.

docs/diagrams/core-approvals.puml

@@ -0,0 +1,46 @@
+@startuml
+interface ApprovalReducer
+interface ApprovalEngine
+interface Projection
+
+class DefaultApprovalReducer
+class DefaultApprovalEngine
+class NoOpApprovalEngine
+class ApprovalProjector
+class DefaultApprovalRepository
+class ApprovalState
+class DomainApprovalRequest
+class ApprovalDecision
+class ApprovalGrant
+class ApprovalContext
+
+ApprovalReducer <|.. DefaultApprovalReducer
+ApprovalEngine <|.. DefaultApprovalEngine
+ApprovalEngine <|.. NoOpApprovalEngine
+Projection <|.. ApprovalProjector
+ApprovalProjector --> ApprovalReducer
+DefaultApprovalRepository --> ApprovalProjector
+DefaultApprovalRepository ..> ApprovalState
+DefaultApprovalState --> "requests" DomainApprovalRequest
+DefaultApprovalState --> "decisions" ApprovalDecision
+DefaultApprovalState --> "grants" ApprovalGrant
+ApprovalDecision --> ApprovalContext
+DefaultApprovalEngine ..> ApprovalGrant
+DefaultApprovalEngine ..> ApprovalDecision
+DefaultApprovalEngine ..> ApprovalContext
+
+package "core:events" <<External>> {
+  [ApprovalRequestedEvent]
+  [ApprovalDecisionResolvedEvent]
+  [ApprovalGrantCreatedEvent]
+  [ApprovalGrantExpiredEvent]
+}
+package "core:sessions" <<External>> {
+  [Projection]
+  [EventReplayer]
+}
+DefaultApprovalReducer ..> "core:events"
+DefaultApprovalRepository ..> "core:events"
+DefaultApprovalRepository ..> "core:sessions"
+
+@enduml