Add CockroachDB/MSSQL CLI support, fix doctor --gaps, and reduce CI fanout

[dmedovich]

Summary

This PR brings the CLI and docs back in sync with the supported driver matrix, tightens
doctor --gaps semantics, and reduces unnecessary CI runs for driver-scoped changes.

Changes

CLI driver support

• add cockroachdb support to the CLI driver factory
• add mssql support to the CLI driver factory
• add sqlserver alias for MSSQL SQL driver resolution
• update CLI help text and init scaffolding so supported drivers are documented
  consistently
• add DSN examples for CockroachDB and MSSQL in init

Doctor command

• make doctor --gaps a true gaps-only mode
• keep default doctor behavior unchanged for the full health-check flow
• add focused tests for doctor result collection behavior

Follow-ups

• CLI refactor remains intentionally out of scope
• full append-only audit logging is intentionally deferred to a future change

Release Notes
Title:
v0.6.0