fix(ci): upgrade to build-push-action@v6, disable sbom

- Upgrade docker/build-push-action from v5 to v6
- Add sbom: false alongside provenance: false
- Update registry URL to internal domain

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -432,7 +432,7 @@ For LLM agent development guidelines and architectural decisions, see [AGENTS.md
 
 ## Version
 
-Current version: **1.2.2** - CI fix
+Current version: **1.2.3** - CI fix
 
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