docs(json): align JSON documentation, examples, and public behavior

[GaspardKirira]

Summary

Review the JSON documentation and examples to ensure they match the final public contracts.

Current behavior

The module contains extensive header documentation, a README, examples, benchmark reports, and a changelog.

Some behavior requires clearer or unified documentation, including:

• Simple ownership and copy semantics;
• integer range behavior;
• JPath mutation behavior;
• file replacement guarantees;
• safe API error suppression;
• ordered versus unordered builders;
• literal macro configuration;
• parsing and serialization limits.

Expected behavior

Users should be able to understand the module’s two JSON models and choose the correct API without reading implementation details.

Scope

• Explain Json versus Simple.
• Explain when to use each model.
• Document Simple ownership semantics.
• Document numeric limits.
• Document JPath read and write differences.
• Document file-write guarantees.
• Document safe and strict error models.
• Document builder return types.
• Document dependency requirements.
• Update examples.
• Remove outdated version strings.
• Verify every example builds.

Suggested files

• modules/json/README.md
• modules/json/CHANGELOG.md
• modules/json/include/vix/json/*.hpp
• modules/json/examples/...
• modules/json/benchmarks/README.md

Acceptance criteria

• The two data models are clearly distinguished.
• Every public helper is documented.
• Examples match current APIs.
• Version references are current or version-independent.
• Dangerous behavior and limits are visible.
• Every documented example compiles.
• Standalone installation instructions work.

Non-goals

This issue does not include:

• redesigning public APIs;
• translating documentation;
• adding unrelated tutorials;
• performance implementation changes.