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-workflow.puml

@@ -0,0 +1,22 @@
+@startuml
+!theme plain
+package "infra-workflow" {
+  interface WorkflowLoader
+  class TomlWorkflowLoader
+  class ConditionSpec
+  class ConditionFactory
+  interface PromptLoader
+  class FileSystemPromptLoader
+  class PromptNotFoundException
+  class WorkflowValidationException
+}
+interface WorkflowGraph <<core:transitions>>
+WorkflowLoader --> WorkflowGraph : load()
+WorkflowLoader <|.. TomlWorkflowLoader
+TomlWorkflowLoader --> ConditionSpec : parses
+TomlWorkflowLoader --> ConditionFactory : uses
+ConditionFactory --> ConditionSpec : converts
+PromptLoader <|.. FileSystemPromptLoader
+TommWorkflowLoader --> WorkflowValidationException : throws
+FileSystemPromptLoader --> PromptNotFoundException : throws
+@enduml