Read CI env from Infisical and give the local stack its own ports

CI reads Infisical staging as the read-only convexmonorepo-base-ci machine identity, runs the quality gate, and builds and pushes the image. The template is not deployed, so there is no Convex or VPS deploy step. The local stack moves to its own Compose name and ports so it runs beside the Payload template's, and it syncs the Convex runtime env. The scripts pick up Infisical account switching, dev-kill and a cache-safe CI install.

.gitignore

@@ -66,3 +66,6 @@ apps/next/playwright-report/
 
 # tanstack
 .tanstack
+
+# local command flags (machine-specific, e.g. which Infisical account to use)
+scripts/flags/