feat: add gr2 repo status surface

[laynepenney]

Summary

• add a read-only gr2 repo status surface across shared repos and unit repos
• classify repo-maintenance state with explicit actions instead of implicit sync behavior
• add focused CLI coverage for missing, dirty, and behind-upstream cases

Closes #545.

Behavior

• inspects shared repos and unit-mounted repos from the live workspace spec
• reports actions such as clone_missing, block_dirty, fast_forward, manual_sync, and no_change
• intentionally does not fetch remotes in this first slice; ahead/behind is based on already-known upstream state

Verification

• cargo check -p gr2-cli --quiet
• cargo test --test cli_tests test_gr2_repo_status_reports_missing_unit_checkout_as_clone_missing --quiet
• cargo test --test cli_tests test_gr2_repo_status_reports_dirty_unit_repo_as_block_dirty --quiet
• cargo test --test cli_tests test_gr2_repo_status_reports_shared_repo_behind_upstream_as_fast_forward --quiet

[laynepenney]

Reviewed locally after the format miss. No new design blocker in this slice: read-only gr2 repo status is the right first surface, and keeping remote fetch out of v1 is the correct boundary. I am pushing the fmt-only fix now, then this can merge once main checks are green.

[laynepenney]

Fixed the CI fallout on : the staging test repos now configure git identity, the shared-repo update test no longer hardcodes , and Windows TOML paths are escaped via . Local verification is green with
running 87 tests
....................................................................................... 87/87

test result: ok. 87 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 5.27s.