fix(clickhouse): strip virtual catalogs from executed queries and inserts

[mday-io]

Description

Fix direct SELECT and INSERT execution when ClickHouse references include SQLMesh's synthetic gateway catalog.

• Render __gw__.db.table as db.table, including qualified columns.
• Preserve the caller's expression, unrelated catalogs, and literal values.
• Extend the view-creation handling from fix(clickhouse): strip virtual catalog from view sources #5940 to direct queries and inserts. Cleanup initialization remains covered by fix(clickhouse): initialize virtual catalog for cleanup #5941.

Test Plan

• make style passes.
• make fast-test: 2,625 passed, four skipped; all 167 isolation tests pass.
• Regression coverage checks SELECT/INSERT references, configured catalog fallback, expression immutability, and unrelated catalogs/literals.
• GitHub CI passes, including ClickHouse integration tests and DCO.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO