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-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://git.zacharyzhang.com/ZacharyZhang-NY/Kigi-CLI/issues";
+pub const FEEDBACK_ISSUES_URL: &str = "https://github.com/ELY-Open-Source/Kigi-CLI/issues/new";
 
 /// HTTP error from the feedback endpoint with a preserved status code, so
 /// callers can distinguish auth failures (401) without string matching.