docs: publish adoption and support guides

[omer-cengel]

Summary

Publish a focused adoption path and support reference for using sqlcj’s packaged CLI and runtime from a Java 21 Maven application without implying public artifact availability.

Changes

• Add a concise README covering prerequisites, locally built artifacts, CLI commands, version compatibility, and the public documentation set.
• Add an end-to-end PostgreSQL quickstart covering generation, compilation, CRUD execution, caller-managed transactions, stale output, and schema-snapshot ownership.
• Document supported query shapes, cardinality, parameters, generated APIs, and unsupported behavior.
• Publish the configuration reference and connect it with the PostgreSQL support documentation.
• Clarify that analysis failures precede output writes while filesystem writes are sequential rather than transactional.

Scope and non-goals

• Documentation only; product code, tests, build configuration, generated files, and supported SQL behavior are unchanged.
• Generation remains a separate CLI step rather than Maven or Gradle lifecycle integration.
• The documented artifacts are locally staged pre-release artifacts; this change does not add licensing, public publication, signing, release automation, or external-sample CI.