BUG: Missing file close error check in Kitty debug logger

[andrinoff]

Describe the bug
Kitty debug logger at fetcher/fetcher.go:2695-2704 writes to file but ignores Close() error. Data may not flush to disk.

To reproduce

1. Set DEBUG_KITTY_LOG to path near disk full
2. Write succeeds but Close() fails
3. Debug data lost silently

Expected behavior
Check Close() error, warn user if write incomplete

Matcha version
master

OS
All

Additional context
File: fetcher/fetcher.go lines 2695-2704
Data loss on close failure