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/core/core-config.adoc

@@ -0,0 +1,89 @@
+= core-config
+
+== purpose
+
+Loads and represents the Correx application configuration from a TOML file. Provides a single entry point (`ConfigLoader`) that reads `~/.config/correx/config.toml` (or a path from `CORREX_CONFIG`) and returns a `CorrexConfig` data class with validated defaults.
+
+== responsibilities
+
+* Read configuration file from well-known filesystem path
+* Parse TOML-format configuration with minimal manual parser
+* Provide type-safe config objects with sensible defaults for all subsystems
+* Silently fall back to defaults when config file is missing or unparseable
+
+== non-responsibilities
+
+* Does not validate configuration values semantically (beyond type coercion)
+* Does not watch for file changes at runtime
+* Does not manage environment variables beyond `CORREX_CONFIG`
+* Does not expose configuration to remote clients
+
+== key types
+
+=== CorrexConfig
+* **kind**: data class
+* **purpose**: Root configuration object, aggregating all subsystem configs.
+* **fields**: `server`, `tui`, `cli`, `approval`, `tools`
+
+=== ServerConfig
+* **kind**: data class
+* **purpose**: Ktor HTTP server binding configuration.
+* **fields**: `host` (default `"localhost"`), `port` (default `8080`)
+
+=== TuiConfig
+* **kind**: data class
+* **purpose**: Terminal UI preferences.
+* **fields**: `theme` (default `"dark"`), `sessionListLimit` (default `5`)
+
+=== CliConfig
+* **kind**: data class
+* **purpose**: CLI output formatting preferences.
+* **fields**: `defaultOutput` (default `"human"`)
+
+=== ApprovalConfig
+* **kind**: data class
+* **purpose**: Approval gate timeouts.
+* **fields**: `timeoutMs` (default `300_000L`)
+
+=== ToolsConfig
+* **kind**: data class
+* **purpose**: Tool sandbox and execution configuration.
+* **fields**: `sandboxRoot`, `workingDir`, `shellAllowedExecutables`, `defaultSystemPromptPath`
+
+=== ConfigLoader
+* **kind**: object
+* **purpose**: Stateless loader that reads and parses the TOML config file.
+* **fields**: none (singleton)
+
+== event flow
+
+*None.* Config is read eagerly at startup and does not participate in event sourcing.
+
+== integration points
+
+* `core:events` — `@Serializable` annotations on all config types
+* `apps:cli`, `apps:server`, `core:approvals`, `core:tools` — consume `CorrexConfig` fields
+
+== invariants
+
+* ConfigLoader must never throw on missing or unparseable files — always returns `CorrexConfig()` with defaults
+* All config types are `@Serializable` for potential persistence
+
+== PlantUML diagram
+
+[plantuml, core-config, "png"]
+----
+include::../../diagrams/core-config.puml[]
+----
+
+
+
+
+== known issues
+
+* TOML parser is hand-written and only supports sections with simple `key = value` pairs. Arrays, inline tables, and multi-line strings are not supported.
+
+== open questions
+
+* Will config be migrated to a proper TOML library (e.g., `ktoml`)?
+* Should config support hot-reload or remain load-once?