Initial template: release pipeline + PORTING.md + init helper

What lands in any repo created from this template:
- .gitea/workflows/release.yml — canonical Gitea-Actions release pipeline
  (tag-triggered, curl-based publish, per-asset failure tolerance)
- tools/build_zip.sh — git-archive per addon folder, multi-addon bundle
- tools/init_from_upstream.sh — one-shot squash-import of upstream tree
  into <AddonFolder>/ at the repo root
- PORTING.md — full CoA-compat bug-pattern checklist (Retail-only
  globals, FileDataIDs, hardcoded class lists, StaticPopup race,
  .tga textures, Minimap mask, CLEU arg positions, Ace3 sweep, etc.)
- README.md — quick-start backport guide
- standard .gitignore (incl dist/) + .gitattributes (* -text)

.gitignore

@@ -0,0 +1,8 @@
+.env
+.DS_Store
+.release
+.install
+.lua/*
+.vscode
+.idea
+dist/