Merging 7 PRs

[jonnii]

This PR merges the following changes:

1. docs: clarify scoped restack agent wording #886 docs: clarify scoped restack agent wording
2. refactor: share PR navigation renderer #887 refactor: share PR navigation renderer
3. refactor: share branch comparison revision resolution #888 refactor: share branch comparison revision resolution
4. refactor: centralize stack graph access #889 refactor: centralize stack graph access
5. refactor: share CLI branch argument resolution #890 refactor: share CLI branch argument resolution
6. refactor: share CLI checkout navigation helpers #891 refactor: share CLI checkout navigation helpers
7. refactor: share best-effort action snapshots #892 refactor: share best-effort action snapshots

Stack

main
  └─ jonnii/20260424222214/clarify-scoped-restack-agent-wording (#886)
    └─ jonnii/20260425165919/share-PR-navigation-renderer (#887)
      └─ jonnii/20260425170438/share-branch-comparison-revision-resolution (#888)
        └─ jonnii/20260425202613/centralize-stack-graph-access (#889)
          └─ jonnii/20260425203354/share-CLI-branch-argument-resolution (#890)
            └─ jonnii/20260425203738/share-CLI-checkout-navigation-helpers (#891)
              └─ jonnii/20260425204205/share-best-effort-action-snapshots (#892)

Stackit-Stack-Size: 7
Stackit-PRs: 886,887,888,889,890,891,892