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-sessions.puml

@@ -0,0 +1,65 @@
+@startuml
+package "core:sessions" {
+  enum SessionStatus {
+    CREATED
+    ACTIVE
+    PAUSED
+    COMPLETED
+    FAILED
+  }
+
+  data class SessionState {
+    + status: SessionStatus
+    + createdAt: Instant?
+    + updatedAt: Instant?
+  }
+
+  data class Session {
+    + sessionId: SessionId
+    + state: SessionState
+  }
+
+  interface SessionReducer {
+    + reduce(SessionState, StoredEvent): SessionState
+  }
+
+  class DefaultSessionReducer
+
+  class SessionProjector
+
+  class DefaultSessionRepository {
+    + getSession(SessionId): Session
+  }
+
+  sealed interface TransitionResult {
+    data class Applied
+    data object Rejected
+  }
+
+  enum ApprovalMode {
+    DENY
+    PROMPT
+    AUTO
+    YOLO
+  }
+
+  DefaultSessionReducer ..|> SessionReducer
+  SessionProjector --> SessionReducer
+  SessionProjector ..|> Projection
+
+  DefaultSessionRepository --> EventReplayer
+  DefaultSessionRepository ..> Session : creates
+  Session *-- SessionState
+}
+
+package ":core:events" as EVENTS {
+  interface Projection
+  interface EventReplayer
+  interface EventStore
+  enum SessionStatus as SES
+}
+
+DefaultSessionRepository --> EVENTS
+SessionProjector --> EVENTS
+
+@enduml