Docs: own and sync ClickHouse documentation

[Blargian]

Summary

Make ClickHouse/clickhouse-java the source of truth for its public ClickHouse documentation.

• Copy the current Java documentation slice from ClickHouse/ClickHouse@21ed77718a5f454680497924d68e9f60a41e026c into docs/clickhouse-docs/, with trailing whitespace normalized. The dedicated subdirectory keeps repository-only engineering docs out of the published slice.
• Add a scoped Mintlify verification workflow for changes to that slice.
• Add a one-way sync workflow that opens or refreshes the corresponding ClickHouse/ClickHouse docs PR after a release, manual dispatch, or merge carrying the sync-docs label.

The published URLs and aggregator path remain unchanged. This does not change the Java API or runtime behavior.

After merge, maintainers should confirm the sync-docs label exists and the Workflow Auth GitHub App credentials are available to this repository.

Validation

• All workflows pass actionlint v1.7.7 and YAML parsing.
• git diff --check passes.
• The migrated slice matches the current aggregator source after trailing-whitespace normalization.
• Compatibility impact: none; documentation and CI only.