[kvlonge]

Why

Phase 3 of the Rust-hosted SQLBuild port (CHI-592): CLI output rendering moves to Rust. This step covers sqb plan (text and JSON) and the plan section printed by sqb build.

Changes

• Plan text and completion formatting in sqlbuild-core cli_text (sections, tree rows, bounded sections, plan document).
• Glue in bindings/_helpers/plan_output/ reads planner objects by attribute; planner logic stays Python.
• New native functions: format_plan, format_plan_json, serialize_future_cursor_safety, serialize_maximum_start_safety.
• Deleted cli/output/_helpers/{plan_text,plan_json,cursor_plan,future_cursor_safety,maximum_start_safety,selection_diagnostics}.py and cli/output/main/{plan,_plan_json}.py.
• Two planner display modules called only from Rust renamed with a leading _.
• Movable Python: 118,042 → 115,330 lines.

Intentional differences: integer microbatch batch_size parsed in Rust; planned batch counts cap at i64::MAX; cursor details are computed for every non-skipped model, including rows beyond the display limit.

Verification

• Real CLI runs on 17 DuckDB projects × 16 plan/build/test variants (text, JSON, colour, verbose, full refresh, after edits): no differences.
• Independent review compared ~9,000 generated plans against the deleted Python: no differences.
• 6,580 focused tests incl. plan e2e; compiler differential; byte-identical 1k compile output; make check-ci; hygiene scan.