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-risk.puml

@@ -0,0 +1,18 @@
+@startuml
+!theme plain
+package "core-risk" {
+  interface RiskAssessor
+  class DefaultRiskAssessor
+  class NoOpRiskAssessor
+  class RiskContext
+  class TierMapping {
+    +toApprovalTier()
+    +toRiskAction()
+  }
+}
+RiskAssessor <|.. DefaultRiskAssessor
+RiskAssessor <|.. NoOpRiskAssessor
+DefaultRiskAssessor --> RiskContext : assess()
+NoOpRiskAssessor --> RiskContext : assess()
+TierMapping --> RiskAssessor : used by
+@enduml