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-router.puml

@@ -0,0 +1,78 @@
+@startuml
+interface RouterFacade
+interface RouterRepository
+interface RouterContextBuilder
+interface RouterReducer
+interface Projection
+
+class DefaultRouterFacade
+class DefaultRouterRepository
+class DefaultRouterContextBuilder
+class DefaultRouterReducer
+class RouterProjector
+
+class RouterState
+class RouterConfig
+class RouterResponse
+class RouterL2Entry
+class RouterTurn
+enum WorkflowStatus
+enum StageOutcomeKind
+enum TurnRole
+enum ChatMode
+
+RouterFacade <|.. DefaultRouterFacade
+RouterRepository <|.. DefaultRouterRepository
+RouterContextBuilder <|.. DefaultRouterContextBuilder
+RouterReducer <|.. DefaultRouterReducer
+Projection <|.. RouterProjector
+RouterProjector --> RouterReducer
+DefaultRouterRepository --> RouterProjector
+DefaultRouterRepository ..> RouterState
+
+DefaultRouterFacade --> RouterRepository
+DefaultRouterFacade --> RouterContextBuilder
+DefaultRouterFacade --> RouterConfig
+DefaultRouterFacade ..> RouterResponse
+DefaultRouterContextBuilder --> RouterConfig
+DefaultRouterContextBuilder --> RouterState
+DefaultRouterContextBuilder ..> "ContextPack"
+
+RouterState --> "l2Memory" RouterL2Entry
+RouterState --> "conversationHistory" RouterTurn
+RouterState --> WorkflowStatus
+RouterL2Entry --> StageOutcomeKind
+RouterTurn --> TurnRole
+
+package "core:events" <<External>> {
+  [EventStore]
+  [SteeringNoteAddedEvent]
+  [WorkflowStartedEvent]
+  [WorkflowCompletedEvent]
+  [WorkflowFailedEvent]
+  [OrchestrationPausedEvent]
+  [OrchestrationResumedEvent]
+  [StageCompletedEvent]
+  [StageFailedEvent]
+}
+package "core:inference" <<External>> {
+  [InferenceRouter]
+  [InferenceProvider]
+  [InferenceRequest]
+}
+package "core:context" <<External>> {
+  [ContextPack]
+}
+package "core:sessions" <<External>> {
+  [Projection]
+  [EventReplayer]
+}
+
+DefaultRouterFacade ..> "core:events"
+DefaultRouterFacade ..> "core:inference"
+DefaultRouterContextBuilder ..> "core:context"
+DefaultRouterRepository ..> "core:events"
+DefaultRouterRepository ..> "core:sessions"
+DefaultRouterReducer ..> "core:events"
+
+@enduml