chore: cut GitHub, make netswitch Gitea-only

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

README.md

@@ -1,6 +1,6 @@
 # netswitch
 
-[![Latest release](https://img.shields.io/github/v/release/Engelgardt23/netswitch)](https://github.com/Engelgardt23/netswitch/releases/latest)
+[![Latest release](https://img.shields.io/gitea/v/release/engel/netswitch?gitea_url=https%3A%2F%2Fgit.engelgardt23.ru&label=release)](https://git.engelgardt23.ru/engel/netswitch/releases/latest)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
 
 🇺🇸 English | [🇷🇺 Русский](README.ru.md)
@@ -9,13 +9,11 @@ A tiny portable tool to flip a Windows network adapter between a **static IP** a
 
 Built for the recurring engineer chore of "give my laptop NIC 10.10.10.1 so I can talk to a server's BMC" and "now put it back on DHCP so I can have internet again."
 
-> **Made by engelgardt.**
-
 ---
 
 ## Download
 
-Grab the latest release: [**releases page**](https://github.com/Engelgardt23/netswitch/releases/latest).
+Grab the latest release: [**releases page**](https://git.engelgardt23.ru/engel/netswitch/releases/latest).
 The asset is `netswitch-portable-vX.Y.Z.zip` (~30 KB).
 
 ## Run
@@ -34,7 +32,7 @@ Only real, wired physical adapters appear in the picker. Wireless, VPN, virtual,
 
 ## Update check
 
-On every launch the tool calls GitHub's `/releases/latest` (3-second timeout). If a newer version is available, it prints a yellow notice and offers to open the download page in your browser. If you're offline, it stays silent.
+On every launch the tool calls the Gitea instance's `/releases/latest` (3-second timeout). If a newer version is available, it prints a yellow notice and offers to open the download page in your browser. If you're offline, it stays silent.
 
 ## Build from source