Shkarko GitButler 0.20.4

ReleaseNotes: |-
## Agentic Use

There is now a new command `but agent setup` which makes the overall setup easier. It is an interactive wizard for tuning version control behavior (similar to https://docs.gitbutler.com/ai-agents/tuning-agent-behavior but easier to setup). Running this is a good idea for best performance.

- Multi-committing, amending and splitting of commits now complete quicker and use less tokens
- Improved PR stacking workflows

## Changes

- There is now a "Font size" setting for the diff views (Settings → Appearance)

## CLI

- `but amend` now accepts `--changes` to amend specific changes into a commit
- You can now provide a message when creating an empty commit with `but commit`
- `but uncommit` now supports a diff output option to print the resulting changes
- `but status` now shows stacked branches that have been merged upstream
- Hunk IDs are now stable across commits and discards
- `but completions` now appears in the help output, making it discoverable when you grab the `but` binary without an installer
- `but` output now labels "unassigned changes" as "uncommitted"
- Fixes a bug where `but apply` could report success while leaving a branch unapplied when workspace metadata was stale
- Removed the `but mark` and `but unmark` commands
- Improved error messages when `stdin` isn't a terminal

## TUI

- You can now reorder stacks in the TUI
- You can now apply branches from the TUI
- You can now move multiple commits at once in the TUI
- You can now commit above or below the selected commit in the TUI
- You can now copy more things in the TUI — commit details, diff hunks, branch names and more — with `shift+y`
- Improved scroll keybindings: `j`/`k`/arrows move by line, `ctrl+d`/`ctrl+u` jump by 10 lines, and `shift+j`/`shift+k` jump by section
- Unapplying a branch and undoing no longer prompt for confirmation in the TUI, since both can be undone

## Fixes

- Fixes a bug where moving empty branches did not work correctly
- Fixes a bug where commit-message and branch-name generation failed for non-OpenAI providers (Anthropic, Ollama, and others)
- Fixes an issue where commit signing failed when `gpg.ssh.program` pointed at a path containing a tilde (`~`)
- Fixes an issue where being offline produced repeated error toasts from background pull-request polling
- Fixes an issue where updating the workspace was not handling squash-merge integrated branches properly
ReleaseNotesUrl: https://github.com/gitbutlerapp/gitbutler/releases