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/app-server.puml

@@ -0,0 +1,42 @@
+@startuml
+package "Server Module" {
+  [ServerModule] as SM
+  [GlobalStreamHandler] as GSH
+  [SessionStreamHandler] as SSH
+  [ApprovalCoordinator] as AC
+  [DomainEventMapper] as DEM
+  [LoggingEventStore] as LES
+  [SessionEventBridge] as SEB
+}
+
+package "Core Domain" {
+  [DefaultSessionOrchestrator] as DSO
+  [EventStore] as ES
+}
+
+package "Infrastructure" {
+  [DefaultProviderRegistry] as DPR
+  [ToolExecutor] as TE
+  [FileSystemWorkflowRegistry] as FSWR
+}
+
+SM --> LES : decorates
+SM --> DSO : orchestrator
+SM --> FSWR : workflowRegistry
+SM --> AC : creates
+SM --> ES : subscribeAll
+
+GSH --> SM : reads registries
+GSH --> DEM : map events
+GSH --> SEB : replaySnapshot
+
+SSH --> AC : registerClient
+SSH --> DEM : map events
+SSH --> DSO : cancel
+
+AC --> DSO : submitApprovalDecision
+AC --> SM.moduleScope : timeout jobs
+
+LES --> ES : delegates
+
+@enduml