fix(core): export the Project block in the DBML exporter - #1034

Summary

• DbmlExporter did not write the Project block, so exporting DBML to DBML dropped the project name, database_type and Note. The example from the issue returned an empty string.
• The exporter now writes the Project block first, with the name (when there is one), database_type and Note. Values are escaped with the existing escapeNote, so the output parses back to the same project. A file without a Project gives the same output as before.
• SQL importers and the db connectors don't set project info, so their DBML output does not change.

Example:

Project "project_name" {
  database_type: 'PostgreSQL'
  Note: 'Description of the project'
}

Issue

#285

Lasting Changes (Technical)

• Added DbmlExporter.exportProject.
• The table_group_settings exporter fixture has a project (name: "a", database_type: "aaa'hehe"), so its expected output now starts with the Project block.
• Not covered here: the JSON from exporter.export(..., 'json') is the normalized model, which importer.import(..., 'json') can't read back, so that path still fails before reaching the exporter. Passing the normalized JSON to ModelExporter.export(..., 'dbml') now keeps the project.

Checklist

• Documentation (if necessary)
• Updated dbml-homepage/static/llms.txt (if docs/features changed)
• Lint Checks Passed
• Unit Tests Passed
• Coverage Tests Passed
• Integration Tests Passed
• Code Review

Docs and llms.txt don't need changes since the syntax is the same. @dbml/core tests: 454 passed. The new tests and the updated fixture fail without the change. In @dbml/cli, the 4 db2dbml tests fail the same way on master in my environment because they need live databases.