Enhance exported source navigation and workbench panels

[forhappy]

Summary

• preserve VS Code source opening while adding commit-pinned GitHub, GitLab, and Bitbucket line links to standalone HTML exports
• validate repository-relative paths, immutable revisions, Git repository ownership, commit availability, and recognized origin remotes before publishing navigation metadata
• use the correct base or target revision when opening source from historical comparisons
• make the left navigation rail collapsible and consolidate repository identity there, removing the duplicated inspector heading to reclaim vertical space
• update compatibility notes, export documentation, generated viewer assets, and regression coverage

Why

Standalone exports previously emitted only the local compass:open-source event, so browsers had no useful destination outside the VS Code host. The workbench also duplicated product and repository identity across both side panels, consuming inspector and community space.

Impact

VS Code behavior remains unchanged. Standalone exports open immutable remote source ranges only when Compass can prove a supported origin and the graph's exact source commit; otherwise source navigation fails safely without inventing a link. The workbench JSON schema remains unchanged because the optional navigation metadata is embedded separately in HTML.

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --lib --bins --locked -- -D warnings
• cargo test --workspace --lib --bins --locked
• cargo test -p compass-output --lib --locked
• cargo test -p compass-cli --test viewer_export_cli html_export_embeds_one_workbench_for_multiple_views --locked
• npm run typecheck:js
• viewer and VS Code unit suites (315 tests)
• focused source-link/workbench tests after rebase (7 tests)
• relevant Playwright accessibility/interaction coverage
• node scripts/check_viewer_assets.mjs
• sh scripts/check_product_boundary.sh