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/infra-tools.puml

@@ -0,0 +1,31 @@
+@startuml
+!theme plain
+package "infra-tools" {
+  class SandboxedToolExecutor
+  class DispatchingToolExecutor
+  class DefaultToolRegistry
+  class ShellTool
+  class DiffUtil
+  class ToolConfig
+  class ShellConfig
+  class FileReadConfig
+  class FileWriteConfig
+  class FileEditConfig
+}
+interface ToolExecutor <<core:tools>>
+interface ToolRegistry <<core:tools>>
+interface Tool <<core:tools>>
+ToolExecutor <|.. SandboxedToolExecutor
+ToolExecutor <|.. DispatchingToolExecutor
+ToolExecutor <|.. ShellTool
+ToolRegistry <|.. DefaultToolRegistry
+Tool <|.. ShellTool
+SandboxedToolExecutor --> ToolRegistry : resolves
+SandboxedToolExecutor --> ToolExecutor : delegates to
+DispatchingToolExecutor --> ToolRegistry : resolves
+SandboxedToolExecutor --> DiffUtil : uses
+ToolConfig --> ShellConfig
+ToolConfig --> FileReadConfig
+ToolConfig --> FileWriteConfig
+ToolConfig --> FileEditConfig
+@enduml