chore: prepare for release v0.4.2

[litedatum]

This issue covers updating all user-facing documentation to reflect the significant CLI changes and new features introduced in the v0.4.2 release. Clear
documentation is critical for user adoption.

Depends on: Completion of Issues #26 and #27.

Acceptance Criteria:

• All examples in docs/usage.md are rewritten to use the new --conn and --table argument format.
• The new multi-table JSON format for the schema command is clearly documented with an example.
• Any quick-start or usage examples in README.md are updated.
• The output of vlite check --help and vlite schema --help is verified to be accurate and clear.

Resolve #28