Move releases, self-update and links to ELY-Open-Source on GitHub

- kigi-env: update_base_url defaults to
  api.github.com/repos/ELY-Open-Source/Kigi-CLI/releases.
- install.sh / install.ps1: resolve releases from the same API.
- /feedback and the no-session feedback fallback open GitHub issues/new;
  /docs opens the README on GitHub.
- SECURITY, NOTICE, AGENTS, CONTRIBUTING: GitHub repo, issues and fork-based
  pull requests replace git.zacharyzhang.com and AGit.

Co-Authored-By: Claude <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://git.zacharyzhang.com/api/v1/repos/ZacharyZhang-NY/Kigi-CLI/releases",
+    update_base_url: "https://api.github.com/repos/ELY-Open-Source/Kigi-CLI/releases",
     upgrade_page_url: "https://www.kimi.com/code/",
 };