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-filesystem.puml

@@ -0,0 +1,19 @@
+@startuml
+!theme plain
+package "infra-tools-filesystem" {
+  class FileReadTool
+  class FileWriteTool
+  class FileEditTool
+}
+interface Tool <<core:tools>>
+interface ToolExecutor <<core:tools>>
+interface FileAffectingTool <<core:tools>>
+Tool <|.. FileReadTool
+Tool <|.. FileWriteTool
+Tool <|.. FileEditTool
+ToolExecutor <|.. FileReadTool
+ToolExecutor <|.. FileWriteTool
+ToolExecutor <|.. FileEditTool
+FileAffectingTool <|.. FileWriteTool
+FileAffectingTool <|.. FileEditTool
+@enduml