Polish drag-to-rebase and add macOS tests

[hewigovens]

Summary

This PR polishes the drag-to-rebase interaction in the DAG, consolidates repo-level presentation surfaces, and adds macOS shell unit coverage.

It also bumps JayJay to 0.2.12 (build 16) and adds a top-level just test-app command that matches the new CI app-test step.

What changed

• implement a custom press/arm/drag state machine for DAG drag-to-rebase
• improve hover targeting and drag affordances in the DAG rows
• split DAG row and DAG view presentation logic into dedicated view models
• consolidate repo alerts, sheets, toast, and loading HUD behind typed presentation state
• add a macOS app test target with regression coverage for drag gesture policy and DAG view models
• run the app tests in CI and expose the same flow through just test-app
• bump app/version metadata to 0.2.12 (build 16)

Validation

• just build
• just test-app

Notes

This is opened as a draft PR so the interaction changes can get one more pass in the app before review.

[gemini-code-assist]

Code Review

This pull request introduces a drag-and-drop rebase feature for the DAG view, allowing users to rebase commits by dragging them onto new parents. It includes a significant refactoring of the presentation layer to use centralized state management for modals, alerts, and toasts, as well as a version bump to 0.2.12 and the addition of macOS app unit tests. Feedback focuses on performance optimizations, specifically regarding unnecessary view redraws from TimelineView, inefficient O(N) lookups during drag operations, and redundant layout calculations within the view's body.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4563a2d832

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".