feat: upgrade to Go 1.25.3 and update build to include api-gateway

- Create ADR-0034 documenting Go version upgrade to 1.25.3
- Mark ADR-0002 as superseded by ADR-0034
- Update CI workflow to use Go 1.25.3
- Update Makefile to build both platform and api-gateway binaries
- Update CI workflow to build and upload both binaries
- Update documentation (ADR README and mkdocs.yml) to include ADR-0034

docs/content/adr/0002-go-version.md

@@ -1,7 +1,7 @@
 # ADR-0002: Go Version
 
 ## Status
-Accepted
+Superseded by [ADR-0034: Go Version Upgrade to 1.25.3](./0034-go-version-upgrade.md)
 
 ## Context
 Go releases new versions regularly with new features, performance improvements, and security fixes. We need to choose a Go version that: