feat: add web asset rebuilding to update command and consolidate post-restart messages

- Detect web/src/** changes and trigger frontend rebuild after updates
- Add buildWebAssets flag to RestartContext and needsWebBuild to UpdateCheckResult
- Consolidate post-restart progress into single editable message
- Delete progress message after completion, show only final result

bot/commands/admin/update.ts

@@ -97,6 +97,7 @@ async function handleUpdate(interaction: any) {
                     timestamp: Date.now(),
                     runMigrations: requirements.needsMigrations,
                     installDependencies: requirements.needsRootInstall || requirements.needsWebInstall,
+                    buildWebAssets: requirements.needsWebBuild,
                     previousCommit: previousCommit.substring(0, 7),
                     newCommit: updateInfo.latestCommit
                 });