chore: cut GitHub, make project Gitea-only

- relink README/CHANGELOG/pyproject/SECURITY to git.engelgardt23.ru
- port CI from GitHub Actions to .gitea/workflows (publishes Gitea release via API)
- rename GITHUB_REPO -> REPO; drop GitHub mentions in code/docs/comments
- remove .github (workflow + issue templates); drop made-by lines

README.md

@@ -1,6 +1,6 @@
 # dhcpsrv
 
-[![Latest release](https://img.shields.io/github/v/release/Engelgardt23/dhcpsrv)](https://github.com/Engelgardt23/dhcpsrv/releases/latest)
+[![Latest release](https://img.shields.io/gitea/v/release/engel/dhcpsrv?gitea_url=https%3A%2F%2Fgit.engelgardt23.ru&label=release)](https://git.engelgardt23.ru/engel/dhcpsrv/releases/latest)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
 
 🇺🇸 English | [🇷🇺 Русский](README.ru.md)
@@ -10,13 +10,11 @@ One double-click — pick a NIC — done. Live table of clients, ping status, pa
 
 Built for the “plug the cable in, watch a BMC pop up with an IP” workflow during firmware updates, recovery, and benchmarks.
 
-> **Made by engelgardt.**
-
 ---
 
 ## Download
 
-Grab the latest release: [**releases page**](https://github.com/Engelgardt23/dhcpsrv/releases/latest).
+Grab the latest release: [**releases page**](https://git.engelgardt23.ru/engel/dhcpsrv/releases/latest).
 The asset is `dhcpsrv-portable-vX.Y.Z.zip` (~12 MB).
 
 ## Run
@@ -39,7 +37,7 @@ The asset is `dhcpsrv-portable-vX.Y.Z.zip` (~12 MB).
 ## What's on screen
 
 ```
-┌─ dhcpsrv v1.0.0  made by engelgardt ────────────────────────────────────┐
+┌─ dhcpsrv v1.0.0 ────────────────────────────────────────────────────────┐
 │ Server: 10.10.10.1/255.255.255.0  Pool: 10.10.10.2–10.10.10.51 …        │
 │ Leases: 3/50  Pkts: 47  DISCOVER: 12  REQUEST: 11  RELEASE: 0           │
 └─────────────────────────────────────────────────────────────────────────┘