chore: start manifest at 6.0.0 to continue from docker hub 5.45.1

The last Docker image published to manifestdotbuild/manifest is tagged
5.45.1 (from 2026-04-09, produced by the old release workflow when the
manifest npm plugin was still being published). Starting the new
canonical packages/manifest version at 0.1.0 would make the next
Docker tag look like a regression on hub.docker.com.

Bump to 6.0.0 because the plugin removal (both manifest and
manifest-model-router) is a genuinely breaking change for anyone still
on the plugin path, so a major bump fits semver semantics and
preserves continuity with the Docker Hub tag sequence.

Author: brunobuddy

packages/manifest/package.json

@@ -1,6 +1,6 @@
 {
   "name": "manifest",
-  "version": "0.1.0",
+  "version": "6.0.0",
   "private": true,
   "description": "Canonical release version for the Manifest Docker image. This package holds no code — the real backend and frontend live in ../backend and ../frontend. See README.md for details."
 }