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-kernel.puml

@@ -0,0 +1,130 @@
+@startuml
+package "core:kernel" {
+  abstract class SessionOrchestrator {
+    # emit()
+    # executeStage()
+    # runInference()
+    # resolveTransition()
+    + abstract run()
+    + abstract cancel()
+  }
+
+  class DefaultSessionOrchestrator {
+    + run()
+    + cancel()
+    + submitApprovalDecision()
+  }
+
+  class ReplayOrchestrator {
+    + run()
+    + cancel()
+    # runInference()
+    # mapValidationOutcome()
+  }
+
+  interface ApprovalGateway {
+    + submitApprovalDecision()
+  }
+
+  interface RetryCoordinator
+  class DefaultRetryCoordinator
+
+  data class OrchestratorRepositories
+  data class OrchestratorEngines
+
+  data class OrchestrationConfig
+  sealed interface WorkflowResult
+  sealed interface ReplayStrategy
+  sealed interface StageOutcome
+  interface OrchestrationReducer
+  class DefaultOrchestrationReducer
+  class OrchestrationProjector
+  class OrchestrationRepository
+
+  class ReplayInferenceProvider
+  class ReplayArtifactMissingException
+
+  DefaultSessionOrchestrator --|> SessionOrchestrator
+  DefaultSessionOrchestrator ..|> ApprovalGateway
+  ReplayOrchestrator --|> SessionOrchestrator
+
+  SessionOrchestrator *-- OrchestratorRepositories
+  SessionOrchestrator *-- OrchestratorEngines
+  SessionOrchestrator --> RetryCoordinator
+
+  DefaultRetryCoordinator ..|> RetryCoordinator
+  DefaultRetryCoordinator --> EventStore
+
+  ReplayOrchestrator --> ReplayInferenceProvider
+
+  OrchestrationProjector --> OrchestrationReducer
+  OrchestrationRepository --> EventReplayer
+}
+
+package "external modules" as EXT {
+  package ":core:events" as EV {
+    interface EventStore
+    interface EventReplayer
+    interface Projection
+  }
+
+  package ":core:sessions" as SES {
+    class DefaultSessionRepository
+    data class Session
+  }
+
+  package ":core:transitions" as TR {
+    interface TransitionResolver
+    data class WorkflowGraph
+    data class StageExecutionResult
+  }
+
+  package ":core:inference" as INF {
+    interface InferenceRouter
+    interface InferenceRepository
+    data class InferenceResponse
+  }
+
+  package ":core:context" as CTX {
+    interface ContextPackBuilder
+  }
+
+  package ":core:validation" as VAL {
+    interface ValidationPipeline
+  }
+
+  package ":core:approvals" as APR {
+    class DefaultApprovalRepository
+  }
+
+  package ":core:risk" as RSK {
+    interface RiskAssessor
+  }
+
+  package ":core:tools" as TOL {
+    interface ToolExecutor
+    interface ToolRegistry
+  }
+
+  package ":core:artifacts-store" as AST {
+    interface ArtifactStore
+  }
+}
+
+SessionOrchestrator --> EV
+SessionOrchestrator --> SES
+SessionOrchestrator --> TR
+SessionOrchestrator --> INF
+SessionOrchestrator --> CTX
+SessionOrchestrator --> VAL
+SessionOrchestrator --> APR
+SessionOrchestrator --> RSK
+SessionOrchestrator --> TOL
+SessionOrchestrator --> AST
+
+ReplayOrchestrator --> EXT
+
+note top of DefaultSessionOrchestrator : Live execution with\nreal inference, validation,\nrisk assessment, approvals
+note top of ReplayOrchestrator : Deterministic replay from\nevent log only
+
+@enduml