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-tui/src/slash/commands/docs.rs

@@ -10,7 +10,7 @@ use crate::slash::command::{AppCtx, ArgItem, CommandExecCtx, CommandResult, Slas
 
 /// Online docs landing page (hardcoded like other TUI deep-links; the
 /// project README is the docs entry point for the repo-hosted docs).
-pub const BUILD_DOCS_URL: &str = "https://github.com/ZacharyZhang-NY/Kigi-CLI/blob/main/README.md";
+pub const BUILD_DOCS_URL: &str = "https://git.zacharyzhang.com/ZacharyZhang-NY/Kigi-CLI/src/branch/main/README.md";
 
 /// Open How-to Guides or online Build docs.
 pub struct DocsCommand;

crates/codegen/kigi-tui/src/slash/commands/feedback.rs

@@ -6,7 +6,7 @@ use crate::slash::command::{CommandExecCtx, CommandResult, SlashCommand};
 /// Where feedback goes: the project's own issue tracker. Kigi is a community
 /// build, so its feedback belongs on its own repo — mirroring the official
 /// kimi-cli, whose `/feedback` opens its repo's issues page.
-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";
 
 /// Open the Kigi issue tracker in the browser.
 pub struct FeedbackCommand;