Use random port for stackblitz

Editor assessment

The subject states the change and its environment exactly — a random port is used for stackblitz — so the header communicates the fix and the hosted context that demands it without the diff, and fix(nitro) classifies and locates it correctly. Hygiene is clean: imperative mood, no trailing period, sensible length, no ticket junk. No body is needed for a contained port-selection fix, and no footer is required. A line on the port conflicts the fixed port caused in the sandbox would add depth; the message is already clear and publishable.