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- Mark ADR-0002 as superseded by ADR-0034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/mkdocs.yml

@@ -95,6 +95,7 @@ nav:
     - "Epic 0: Project Setup & Foundation":
       - "ADR-0001: Go Module Path": adr/0001-go-module-path.md
       - "ADR-0002: Go Version": adr/0002-go-version.md
+      - "ADR-0034: Go Version Upgrade to 1.25.3": adr/0034-go-version-upgrade.md
       - "ADR-0003: Dependency Injection Framework": adr/0003-dependency-injection-framework.md
       - "ADR-0004: Configuration Management": adr/0004-configuration-management.md
       - "ADR-0005: Logging Framework": adr/0005-logging-framework.md