feat(config): add semantic loading model

CHANGELOG.md

@@ -10,6 +10,10 @@ All notable changes to this project will be documented in this file.
   corresponding compression feature is enabled.
 - Added a non-public binary log record format and reader research prototype;
   no production binary backend is enabled yet.
+- Added the parser-neutral configuration model, diagnostics, structural
+  validation, and side-effect-free materialization contract for Configuration
+  Loading v1. JSON/properties parsing and logger instantiation remain separate
+  follow-up layers.
 
 ### Fixed
 

docs/adr/0009-configuration-loading-contract.md

@@ -166,5 +166,6 @@ should follow a stable static-load contract rather than constrain it in advance.
 ## References
 
 - [Roadmap: Configuration loading](../future-plans.md)
+- [Parser-neutral model header](../../include/logit_cpp/logit/configuration.hpp)
 - [ADR 0002: Shared and dedicated asynchronous executors](0002-async-executor-model.md)
 - [ADR 0008: Binary log record format research prototype](0008-binary-log-record-format-research.md)

include/logit_cpp/logit.hpp

@@ -11,6 +11,7 @@
 
 #include "logit/config.hpp"
 #include "logit/enums.hpp"
+#include "logit/configuration.hpp"
 #include "logit/utils.hpp"
 #include "logit/formatter.hpp"
 #include "logit/loggers.hpp"