chore: bump next to 1.5.1-dev.0

Move next onto the -dev prerelease stream after the v1.5.0 release per
ADR-660 (next must not rest at the last-released version).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@opengsd/gsd-core",
-  "version": "1.5.0",
+  "version": "1.5.1-dev.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@opengsd/gsd-core",
-      "version": "1.5.0",
+      "version": "1.5.1-dev.0",
       "license": "MIT",
       "dependencies": {
         "@anthropic-ai/claude-agent-sdk": "^0.2.84",