fix ci: calver suffix must be .N not +N so docker tags stay valid

the gitea workflow tags the image with the package.json version; docker oci
refs forbid '+', so 2026.04.13+2 broke buildx with "invalid reference format".
switch to 2026.04.13.3. this matches what project memory already documented;
the global AGENTS.md example using +n doesn't apply here because we ship via
a registry.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "netfelix-audio-fix",
-	"version": "2026.04.13+2",
+	"version": "2026.04.13.3",
 	"scripts": {
 		"dev:server": "NODE_ENV=development bun --hot server/index.tsx",
 		"dev:client": "vite",