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/modules/infrastructure/infra-security.adoc

@@ -0,0 +1,54 @@
+= infra-security
+
+== purpose
+
+Placeholder module reserved for security infrastructure — authentication, authorization, credential management, and secure communication. Currently contains only a `Module` marker object with no implementation.
+
+== responsibilities
+
+* Intended: provide authentication adapters (API keys, OAuth, etc.)
+* Intended: enforce authorization checks on tool execution and API access
+* Intended: manage credential storage and rotation
+
+== non-responsibilities
+
+* Does not define security contracts — that belongs to `core`
+* Does not implement approval gates — that belongs to `core:approvals`
+* Does not provide sandboxing — that belongs to `infra:tools`
+
+== key types
+
+=== Module
+* **kind**: object
+* **purpose**: Module marker for the Gradle subproject; no behavior.
+
+== event flow
+
+*None.* No events are consumed or emitted. This is a placeholder.
+
+== integration points
+
+No integration points. The module has no dependencies beyond `core:events`.
+
+== invariants
+
+None — module is empty.
+
+== PlantUML diagram
+
+[plantuml, infra-security, "png"]
+----
+include::../../diagrams/infra-security.puml[]
+----
+
+
+
+
+== known issues
+
+Module is a placeholder — no security infrastructure exists.
+
+== open questions
+
+* What authentication mechanism(s) will be supported (API key, JWT, mTLS)?
+* Will credentials be stored in the event store or in an external secrets manager?