Package and distribute signed desktop applications

## Problem

Installing a Python package through Homebrew or uv is appropriate for terminal users but does not provide the normal download-and-launch experience expected from a graphical desktop application.

## Proposed change

Extend the release workflow to build, sign, package, and publish native desktop artifacts. Evaluate `pyside6-deploy` as the primary deployment tool and document any evidence-based reason for selecting another tool.

Continue publishing the existing Python and Homebrew distributions for TUI users.

## Acceptance Criteria

- [ ] Release CI builds the GUI natively on macOS and Windows.
- [ ] macOS releases provide a signed and notarized application in a user-friendly distribution container such as a DMG.
- [ ] Windows releases provide a signed graphical installer.
- [ ] QML modules, Qt plugins, Python dependencies, assets, fonts, and application metadata are bundled explicitly.
- [ ] Desktop artifacts use the same version and intentional release tag as the Python distribution.
- [ ] Existing PyPI and Homebrew TUI releases continue to work.
- [ ] Fresh-machine verification covers installation, launch, Arena log discovery, the representative live workflow, upgrade behavior, and uninstallation.
- [ ] Installation, troubleshooting, and release procedures are documented.
- [ ] Mobile delivery, app-store publication, automatic updates, and Linux-native installers remain outside this ticket unless separately approved.