chore: bump version to 6.0.0-alpha.12 and add yaml dependency

- Add missing yaml package dependency to fix MODULE_NOT_FOUND error
- Update CHANGELOG.md with alpha.12 release notes

package-lock.json

@@ -24,7 +24,8 @@
         "ora": "^5.4.1",
         "semver": "^7.6.3",
         "wrap-ansi": "^7.0.0",
-        "xml2js": "^0.6.2"
+        "xml2js": "^0.6.2",
+        "yaml": "^2.7.0"
       },
       "bin": {
         "bmad": "tools/bmad-npx-wrapper.js",
@@ -8441,7 +8442,6 @@
       "version": "2.8.1",
       "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.8.1.tgz",
       "integrity": "sha512-lcYcMxX2PO9XMGvAJkJ3OsNMw+/7FKes7/hgerGUYWIoWu5j/+YQqcZr5JnPZWzOsEBgMbSbiSTn/dv/69Mkpw==",
-      "dev": true,
       "license": "ISC",
       "bin": {
         "yaml": "bin.mjs"