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-shell/src/agent/feedback_client.rs

@@ -12,7 +12,7 @@ use std::sync::Arc;
 use serde::Serialize;
 
 /// Where non-subscription users (no OAuth session) submit feedback instead.
-pub const FEEDBACK_ISSUES_URL: &str = "https://github.com/ZacharyZhang-NY/Kigi-CLI/issues";
+pub const FEEDBACK_ISSUES_URL: &str = "https://git.zacharyzhang.com/ZacharyZhang-NY/Kigi-CLI/issues";
 
 /// HTTP error from the feedback endpoint with a preserved status code, so
 /// callers can distinguish auth failures (401) without string matching.