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.

docker-compose.yml

@@ -3,16 +3,16 @@ services:
     build:
       context: .
       dockerfile: Dockerfile
-    container_name: upkeep
+    container_name: uptop
     restart: unless-stopped
     ports:
       - "23234:23234"
       - "8080:8080"
     environment:
-      - UPKEEP_DB_TYPE=sqlite
-      - UPKEEP_DB_DSN=/data/upkeep.db
-      - UPKEEP_HTTP_PORT=8080
-      - UPKEEP_STATUS_ENABLED=true
-      - UPKEEP_STATUS_TITLE=System Status
+      - UPTOP_DB_TYPE=sqlite
+      - UPTOP_DB_DSN=/data/uptop.db
+      - UPTOP_HTTP_PORT=8080
+      - UPTOP_STATUS_ENABLED=true
+      - UPTOP_STATUS_TITLE=System Status
     volumes:
       - ./data:/data