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-tools.puml

@@ -0,0 +1,51 @@
+@startuml
+interface Tool
+interface FileAffectingTool
+interface ToolExecutor
+interface ToolRegistry
+interface ToolReducer
+interface Projection
+
+class DefaultToolReducer
+class ToolProjector
+class DefaultToolRepository
+
+class ToolState
+class ToolInvocationRecord
+class ValidationResult
+enum ToolInvocationStatus
+enum ToolCapability
+
+Tool <|-- FileAffectingTool
+ToolReducer <|.. DefaultToolReducer
+Projection <|.. ToolProjector
+ToolProjector --> ToolReducer
+DefaultToolRepository --> ToolProjector
+DefaultToolRepository ..> ToolState
+ToolState --> "invocations" ToolInvocationRecord
+ToolInvocationRecord --> ToolInvocationStatus
+
+package "core:events" <<External>> {
+  [ToolInvocationRequestedEvent]
+  [ToolExecutionStartedEvent]
+  [ToolExecutionCompletedEvent]
+  [ToolExecutionFailedEvent]
+  [ToolExecutionRejectedEvent]
+  [ToolRequest]
+  [ToolReceipt]
+}
+package "core:approvals" <<External>> {
+  [Tier]
+}
+package "core:sessions" <<External>> {
+  [Projection]
+  [EventReplayer]
+}
+
+DefaultToolReducer ..> "core:events"
+DefaultToolRepository ..> "core:events"
+DefaultToolRepository ..> "core:sessions"
+Tool ..> "core:events"
+Tool ..> "core:approvals"
+
+@enduml