fix(tui): avoid OSC52 success on XTerminal

[chaochaoweb3]

Summary

• Skip OSC 52 clipboard writes when running in XTerminal
• Preserve existing optimistic behavior for terminals where OSC 52 was attempted
• Let fallback clipboard failures surface when OSC 52 was not attempted, so the TUI shows the existing failure toast instead of a false success

Fixes #188.

Verification

• git diff --check
• Attempted module import with local Bun; blocked by incomplete local dependency install (isexe missing from which) in this checkout

[qiaozongming]

#957

[qiaozongming]

#1104