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-context.puml

@@ -0,0 +1,58 @@
+@startuml
+interface ContextPackBuilder
+interface DecisionPointBuilder
+interface ContextCompressor
+interface ContextReducer
+interface Projection
+
+class DefaultContextPackBuilder
+class DefaultDecisionPointBuilder
+class DefaultContextCompressor
+class DefaultContextReducer
+class ContextProjector
+class DefaultContextRepository
+
+class ContextPack
+class ContextEntry
+class ContextLayer
+class TokenBudget
+class CompressionMetadata
+class CompressionStrategy
+class SteeringNote
+class ContextState
+
+ContextPackBuilder <|.. DefaultContextPackBuilder
+DecisionPointBuilder <|.. DefaultDecisionPointBuilder
+ContextCompressor <|.. DefaultContextCompressor
+ContextReducer <|.. DefaultContextReducer
+Projection <|.. ContextProjector
+ContextProjector --> ContextReducer
+DefaultContextRepository --> ContextProjector
+
+DefaultContextPackBuilder --> ContextCompressor
+DefaultContextPackBuilder ..> ContextPack
+DefaultContextPackBuilder --> TokenBudget
+ContextPack --> "layers" ContextLayer
+ContextPack --> "entries" ContextEntry
+ContextPack --> CompressionMetadata
+DefaultContextCompressor --> CompressionStrategy
+DefaultContextCompressor --> TokenBudget
+DefaultDecisionPointBuilder ..> ContextPack
+DefaultDecisionPointBuilder --> ContextEntry
+
+package "core:events" <<External>> {
+  [ContextBuildingStartedEvent]
+  [ContextPackBuiltEvent]
+  [ContextBuildingFailedEvent]
+  [ContextBuildingInterruptedEvent]
+}
+package "core:sessions" <<External>> {
+  [Projection]
+  [EventReplayer]
+}
+
+DefaultContextReducer ..> "core:events"
+DefaultContextRepository ..> "core:events"
+DefaultContextRepository ..> "core:sessions"
+
+@enduml