chore: cut GitHub, make vrcx Gitea-only

- relink README/CHANGELOG/pyproject to git.engelgardt23.ru; drop github build badge
- update-check + clone URL point to Gitea; rename GITHUB_REPO -> REPO
- port CI to .gitea/workflows (self-contained, publishes Gitea release)
- remove .github (workflow + issue templates)

README.md

@@ -1,7 +1,6 @@
 # vrcx
 
-[![Latest release](https://img.shields.io/github/v/release/Engelgardt23/vrcx?include_prereleases&label=release)](https://github.com/Engelgardt23/vrcx/releases/latest)
-[![Build](https://img.shields.io/github/actions/workflow/status/Engelgardt23/vrcx/release.yml?label=build)](https://github.com/Engelgardt23/vrcx/actions)
+[![Latest release](https://img.shields.io/gitea/v/release/engel/vrcx?gitea_url=https%3A%2F%2Fgit.engelgardt23.ru&include_prereleases&label=release)](https://git.engelgardt23.ru/engel/vrcx/releases/latest)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
 [![Lang: en \| ru](https://img.shields.io/badge/lang-en%20%7C%20ru-blue)](#)
 
@@ -22,7 +21,7 @@ The original VRC only touches the BMC. In real incidents support almost always a
 
 ## Download
 
-Grab the latest release: [**releases page**](https://github.com/Engelgardt23/vrcx/releases/latest).
+Grab the latest release: [**releases page**](https://git.engelgardt23.ru/engel/vrcx/releases/latest).
 The asset is `vrcx-portable-vX.Y.Z.zip`.
 
 ## Run
@@ -86,7 +85,7 @@ Adding a new artefact = one line in the relevant table.
 ## Build from source
 
 ```
-git clone https://github.com/Engelgardt23/vrcx.git
+git clone https://git.engelgardt23.ru/engel/vrcx.git
 cd vrcx
 python -m pip install rich paramiko pyinstaller
 python -m PyInstaller --onefile --console --name vrcx --icon dev/assets/icon.ico --paths dev/src dev/vrcx-launcher.py