Restrict Renovate to the v0 tag scheme for mautrix images

Prevents Renovate from proposing "major" updates to the registry-only
calver tags (vYY.MM[.PATCH]), which break further updates and
self-building. See the previous commit for details.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/renovate.json

@@ -25,6 +25,13 @@
 				"https://github.com/devture/com.devture.ansible.role{/,}**",
 				"https://github.com/mother-of-all-self-hosting{/,}**"
 			]
+		},
+		{
+			"description": "mautrix images are dual-tagged (v0.YYMM.PATCH and vYY.MM[.PATCH]). Stick to the v0 scheme: it matches the git tags (needed for self-building) and has a consistent number of components (the calver tags do not, which makes Renovate stop offering updates).",
+			"matchPackageNames": [
+				"dock.mau.dev/mautrix/**"
+			],
+			"allowedVersions": "/^v0\\./"
 		}
 	],
 	"pre-commit": {