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

The GitHub account is restored, so github.com/ZacharyZhang-NY/Kigi-CLI is
the canonical repo again. Reverse the 2026-08 Gitea migration:

- .github/workflows/{release,warm-cache}.yml: restore the GitHub-hosted
  pipeline dropped in 3e1652c, unchanged — hosted runners, rust-cache,
  softprops release with every asset attached atomically.
- .gitea/workflows/release.yml: retire the Gitea edition (the runners are
  being deregistered; git.zacharyzhang.com keeps the v0.1.12/v0.1.13
  releases for old clients).
- kigi-env: update_base_url now defaults to the GitHub Releases API. The
  updater already speaks GitHub wire format and sends a User-Agent; v0.1.14
  is published to BOTH forges with identical assets so pre-0.1.14 installs
  polling Gitea self-update onto the GitHub channel.
- install.sh / install.ps1: resolve releases from api.github.com.
- feedback, /docs, SECURITY.md, frontend worker + site: repo, issues and
  raw-file links point at github.com / raw.githubusercontent.com.
- docs/RELEASE.md: GitHub edition of the checklist; Gitea runner sections
  retired.
- version: 0.1.13 -> 0.1.14 (the cross-forge transition release).

Claude-Session: https://claude.ai/code/session_01A6RcwHhhsFYYrNdQB4ASuP

install.sh

@@ -14,15 +14,14 @@
 # Environment:
 #   KIGI_SHARE_DIR        install root (default: ~/.kigi)
 #   KIGI_UPDATE_BASE_URL  releases API base, GitHub/Gitea-shaped (default:
-#                         https://git.zacharyzhang.com/api/v1/repos/ZacharyZhang-NY/Kigi-CLI/releases)
+#                         https://api.github.com/repos/ZacharyZhang-NY/Kigi-CLI/releases)
 #
 # Fails fast on any error; never leaves a partial binary as the active kigi.
 
 set -eu
 
 REPO="ZacharyZhang-NY/Kigi-CLI"
-FORGE="https://git.zacharyzhang.com"
-API_BASE="${KIGI_UPDATE_BASE_URL:-${FORGE}/api/v1/repos/${REPO}/releases}"
+API_BASE="${KIGI_UPDATE_BASE_URL:-https://api.github.com/repos/${REPO}/releases}"
 KIGI_HOME="${KIGI_SHARE_DIR:-$HOME/.kigi}"
 
 err() {