chore: complete rename from go-upkeep to uptop

- Module path: gitea.lerkolabs.com/lerko/uptop
- Binary: cmd/uptop/
- All imports updated to full module path
- Env vars: UPKEEP_* → UPTOP_*
- Prometheus metrics: upkeep_* → uptop_*
- Default DB: uptop.db
- Docker image: lerko/uptop
- All docs, compose files, CI updated

Only remaining "go-upkeep" reference is the fork attribution in README.

.github/workflows/docker.yml

@@ -29,7 +29,7 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ secrets.DOCKERHUB_USERNAME }}/go-upkeep
+          images: ${{ secrets.DOCKERHUB_USERNAME }}/uptop
           tags: |
             # This turns git tag "v1.0.0" into docker tag "1.0.0"
             type=semver,pattern={{version}}