Render diff sidebar as a collapsible file tree

The flat file list got unreadable once paths shared long prefixes.
Build a tree from the changed paths (compressing chains of single-child
dirs like GitHub does), and render each folder with a toggle, plus
Expand all / Collapse all and a per-file comment-count badge.

Default givy diff to show unstaged changes

Running `givy diff` without arguments now behaves the same as
`givy diff @unstaged` instead of comparing against the default branch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Update release skill to support major/minor/patch version bumping

The release skill now accepts "major", "minor", or "patch" as arguments
to automatically bump from the latest tag, in addition to explicit versions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Improve branch selector UX with current branch detection and filtering

- Add isCurrent field to detect the checked-out branch
- Default compare branch to the current branch
- Exclude the other selector's branch from each dropdown
- Preserve branch selection when switching to Unstaged/Staged tabs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Fix E2E test strict mode violations with scoped locators

- Scope file link assertions to file-list testId in changes-view and commit-view
- Scope breadcrumb link assertion to navigation role in file-tree
- Add file-list testId to SimpleDiffViewer sidebar for consistency with DiffViewer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add hot reload for markdown preview with ETag-based polling

Poll the blob API every 1s while in markdown preview mode. The backend
computes a SHA-256 ETag and returns 304 when the file is unchanged,
avoiding unnecessary payload transfer and React re-renders.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add release documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Remove trailing newline from generated untracked file patch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add release GitHub Actions workflow for cross-build binaries

Builds linux/amd64, linux/arm64, darwin/amd64, darwin/arm64 binaries
and uploads them to GitHub Releases when a v* tag is pushed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>