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.

.gitignore

@@ -26,8 +26,8 @@ go.work
 
 # End of https://www.toptal.com/developers/gitignore/api/go
 
-/goupkeep
-upkeep.db
+/uptop
+uptop.db
 
 .ssh
 
@@ -35,8 +35,5 @@ authorized_keys
 
 tmp
 
-# Old repo
-/go-upkeep/
-
 *.local.json
 *.local.md