chore: migrate from Gitea to GitHub

Replace Gitea CI workflow with GitHub Actions workflow using gh CLI
for release creation. Update auto-updater, changelog fetch, download
links, electron-builder publish config, and package.json homepage to
point at github.com/bigjakk/Krunker-Civilian-Client.

README.md

@@ -3,8 +3,8 @@
 > a high-performance krunker client with unlimited FPS, built on a custom-patched Electron
 
 **Download:**
-[Windows (x64)](https://gitea.crjlab.net/bigjakk/Krunker-Civilian-Client/releases/latest) -
-[Linux (AppImage)](https://gitea.crjlab.net/bigjakk/Krunker-Civilian-Client/releases/latest)
+[Windows (x64)](https://github.com/bigjakk/Krunker-Civilian-Client/releases/latest) -
+[Linux (AppImage)](https://github.com/bigjakk/Krunker-Civilian-Client/releases/latest)
 
 ## Features
 
@@ -75,7 +75,7 @@ For details on the patch and build instructions, see [Electron-Websocket-Fix](ht
 1. Install [git](https://git-scm.com/downloads), [Node.js](https://nodejs.org/), and npm
 2. Clone and install:
    ```bash
-   git clone https://gitea.crjlab.net/bigjakk/Krunker-Civilian-Client.git
+   git clone https://github.com/bigjakk/Krunker-Civilian-Client.git
    cd Krunker-Civilian-Client
    npm install
    ```