Initial: MPQ patch packager (Gitea Action, StormLib-based)

A BigWigs-style CI packager for WoW MPQ patch archives. Reads an mpq.yaml
manifest, stages files, builds a vanilla-1.12-compatible patch-X.mpq via
StormLib, and (in the example workflow) attaches it to a Gitea release on tag.

test/fixture/Hello.lua

@@ -0,0 +1,4 @@
+-- Fixture file packed by the CI smoke test. Version token below is substituted
+-- by the packager when substitute.enabled is true.
+local VERSION = "@project-version@"
+print("mpq-packager fixture, version " .. VERSION)

test/mpq.yaml

@@ -0,0 +1,9 @@
+# Manifest used by the CI smoke test.
+name: fixture
+patch-letter: Z
+substitute:
+  enabled: true
+  extensions: [".lua"]
+contents:
+  - src: fixture
+    dest: Interface/AddOns/Fixture