fix: resolve 4 tag-blocking issues for v0.1.0

- README/CONTRIBUTING quick start: add UPTOP_ADMIN_KEY so SSH works on
  fresh DB, fix single-file go run path that doesn't compile
- apply --dry-run: assign placeholder IDs for new alerts and groups so
  resolveAlertID succeeds when monitors reference not-yet-created alerts
- deploy/*.yml: switch user-facing compose files from broken build
  context to image: lerkolabs/uptop:latest, fix dev context to ..

CONTRIBUTING.md

@@ -3,7 +3,7 @@
 ## Development
 
 ```sh
-go run cmd/uptop/main.go -demo  # starts with sample data
+go run ./cmd/uptop -demo        # starts with sample data
 ssh -p 23234 localhost              # connect to TUI
 ```