Return the forge to Gitea: releases, self-update, links, CI

The GitHub account is gone again, so git.zacharyzhang.com/ZacharyZhang-NY/Kigi-CLI
is the canonical repo. Reverse f7a4cb6:

- .gitea/workflows/release.yml: restore the Gitea edition retired in f7a4cb6
  (draft release, per-target upload, SHA256SUMS, then publish). The Windows
  leg runs on the windows-amd64 label the current runner advertises.
- .github/workflows/{release,warm-cache}.yml: drop them; they target hosted
  GitHub runners and softprops, and Gitea ignores them once .gitea exists.
- kigi-env: update_base_url defaults to the Gitea Releases API again.
- install.sh / install.ps1: resolve releases from git.zacharyzhang.com.
- feedback, /docs, SECURITY.md, frontend worker + site: repo, issues and
  raw-file links point at git.zacharyzhang.com.
- docs/RELEASE.md: Gitea edition of the checklist with the current runners.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/codegen/kigi-env/src/lib.rs

@@ -21,7 +21,7 @@ pub struct KigiEndpoints {
 pub const PRODUCTION_ENDPOINTS: KigiEndpoints = KigiEndpoints {
     coding_api_base_url: "https://api.kimi.com/coding/v1",
     oauth_host: "https://auth.kimi.com",
-    update_base_url: "https://api.github.com/repos/ZacharyZhang-NY/Kigi-CLI/releases",
+    update_base_url: "https://git.zacharyzhang.com/api/v1/repos/ZacharyZhang-NY/Kigi-CLI/releases",
     upgrade_page_url: "https://www.kimi.com/code/",
 };