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 ..

deploy/docker-compose.probe.yml

@@ -1,6 +1,6 @@
 services:
   leader:
-    build: .
+    image: lerkolabs/uptop:latest
     environment:
       - UPTOP_CLUSTER_MODE=leader
       - UPTOP_CLUSTER_SECRET=changeme  # EXAMPLE ONLY — rotate before use
@@ -11,7 +11,7 @@ services:
       - "23234:23234"
 
   probe-us-east:
-    build: .
+    image: lerkolabs/uptop:latest
     environment:
       - UPTOP_CLUSTER_MODE=probe
       - UPTOP_NODE_ID=us-east-1
@@ -23,7 +23,7 @@ services:
       - leader
 
   probe-eu-west:
-    build: .
+    image: lerkolabs/uptop:latest
     environment:
       - UPTOP_CLUSTER_MODE=probe
       - UPTOP_NODE_ID=eu-west-1