Reorient CI engine workflows

[nicosuave]

Summary

• Consolidates engine-specific integration coverage into one local-engine matrix with adapter integration and CLI e2e coverage per engine.
• Splits ADBC driver validation into a dedicated dbc-backed driver matrix covering sqlite, duckdb, postgres, clickhouse, bigquery, and snowflake.
• Renames core workflow jobs so Python, Rust, Pyodide, native compat, and DuckDB extension ownership are clearer without dropping coverage.

Validation

Validated with required lint, required format check, the full Python test suite, YAML parse checks, matrix membership checks, and actionlint on the changed workflows.