fix: custom-dir session create used user input not server directory (scope drift)

onCreateInDirectory navigated with dir.trim() (raw user input) while the
sibling create paths use the server-authoritative session.directory. When
the opencode server normalizes the path (trailing slash/symlink/relative),
the nav param diverged from the session's real scope, causing the new
session/[id] screen to scope to the wrong client -> 'Failed to load
session'. Mirror the sibling paths' session.directory spread.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/(tabs)/index.tsx

@@ -215,7 +215,10 @@ export default function SessionsScreen() {
         setShowNewSession(false)
         setCustomDir("")
         if (session) {
-          router.push({ pathname: `/session/[id]`, params: { id: session.id, directory: dir.trim() } })
+          router.push({
+            pathname: `/session/[id]`,
+            params: { id: session.id, ...(session.directory ? { directory: session.directory } : {}) },
+          })
         }
       } catch (error) {
         console.error("Failed to create session in directory:", error)