fix(web): every reconnect gets its own grace period before the unavailable banner - #20441

Eligibility
This single-file, nine-line fix only resets reconnect grace-period state when the active reconnecting environment changes, preventing stale state from suppressing later grace periods. It is a localized UI behavior fix with no schema, configuration, infrastructure, or security impact.

Notes:
No code owners found in target merge base f5cb328