Confirm before Stop / Restart on production web apps

[Copilot]

appService.Stop and appService.Restart executed immediately, so a mis-click in the tree context menu (Stop sits next to Restart) could take a production site down with no confirmation—unlike Delete and Swap Slots, which already gate on a warning modal.

Changes

• stopWebApp.ts: On the production slot (!node.site.isSlot), show a { modal: true } warning gated with DialogResponses.yes/cancel before calling client.stop(). Staging/dev slots are unaffected.
• restartWebApp.ts: Same production-only gate with a restart-specific message. Reworked to run client.stop() → client.start() inline (previously chained the appService.Stop/appService.Start commands) so restart shows a single prompt instead of inheriting Stop's dialog.

if (!node.site.isSlot) {
    const confirmMessage = localize('confirmStop', 'Stop web app "{0}"? Traffic will be interrupted.', node.site.fullName);
    await context.ui.showWarningMessage(confirmMessage, { modal: true, stepName: 'confirmStop' }, DialogResponses.yes, DialogResponses.cancel);
}

Note: isSlot === false is the production site; deployment slots (staging/dev) have isSlot === true, matching the existing convention in ResolvedWebAppResource.ts.