feat(vscode): add multi-command query workbench

[forhappy]

Summary

• replace the single-result VS Code query view with separate Ask, Explain, and CompassQL command modes
• keep up to eight selectable result tabs with command-specific drafts, cancellation, and source/graph actions
• render typed Ask evidence, diagnostics, symbol explanations, relationships, and CompassQL rows as readable UI instead of raw JSON blobs
• add strict compass ask --at REV support for immutable trusted revision graphs; legacy or incompatible revisions must be rebuilt
• update generated viewer assets, compatibility notes, command reference, and VS Code guidance

Verification

• cargo test -p compass-cli --test code_query_cli --locked (17 passed)
• cargo test -p compass-cli --test history_cli current_snapshot_promotion_matches_an_exact_rebuild --locked
• cargo clippy -p compass-cli --all-targets --locked -- -D warnings
• cargo fmt --all -- --check
• npm run typecheck:js
• focused viewer and VS Code query unit tests (14 passed)
• staged-tree Playwright query suite (10 passed)
• full viewer Playwright suite (85 passed)
• node scripts/check_viewer_assets.mjs
• sh scripts/check_product_boundary.sh