fix terminal style (#6056)

## Summary

After #5292, at certain browser zoom levels, the xterm terminal did not
fill horizontal space properly, showing a gap with mismatched background
colors (`#171717` viewport vs `black` terminal content).

Fixes https://github.com/Comfy-Org/ComfyUI_frontend/issues/6049

## Problem

The hardcoded `#171717` terminal theme background only affected the
xterm viewport, while terminal content remained black, causing a visible
color mismatch at low zoom levels where the gap was more apparent.

Fixed by keeping original theme when not on desktop distribution.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6056-fix-terminal-style-28c6d73d36508132b521e5767f41d540)
by [Unito](https://www.unito.io)

src/platform/distribution/types.ts

@@ -1,3 +1,5 @@
+import { isElectron } from '@/utils/envUtil'
+
 /**
  * Distribution types and compile-time constants for managing
  * multi-distribution builds (Desktop, Localhost, Cloud)
@@ -13,6 +15,6 @@ declare global {
 const DISTRIBUTION: Distribution = __DISTRIBUTION__
 
 /** Distribution type checks */
-// const isDesktop = DISTRIBUTION === 'desktop'
-// const isLocalhost = DISTRIBUTION === 'localhost'
+export const isDesktop = DISTRIBUTION === 'desktop' || isElectron() // TODO: replace with build var
 export const isCloud = DISTRIBUTION === 'cloud'
+// export const isLocalhost = !isDesktop && !isCloud