chore(admin-panel): upgrade express to v5
Because: - The admin panel server runs on Express 4 and should move to Express 5. - Express 5 passes app.listen errors to the callback instead of crashing. This commit: - Updates express to ^5.2.1 and @types/express to ^5.0.6. - Gives the heartbeat and version handlers void block bodies. - Rethrows the app.listen callback error so a failed bind still crashes. - Adds a test for the rethrown listen error. Closes FXA-14786