fix(tui): apply path/@ completion on Enter

Completion selection on Enter was gated to slash commands only
(value.startsWith('/')), so @file, ./path, and ~/path completions fell
through and submitted the incomplete input instead of inserting the
highlighted row.

Guard on completions.length && compReplace > 0 — useCompletion already
scopes population to slash and path tokens, and the next !== value check
keeps plain-text submits working when the completion is already applied.

ui-tui/src/__tests__/platform.test.ts

@@ -5,6 +5,7 @@ const originalPlatform = process.platform
 async function importPlatform(platform: NodeJS.Platform) {
   vi.resetModules()
   Object.defineProperty(process, 'platform', { value: platform })
+
   return import('../lib/platform.js')
 }