Fixes apply.rs path parsing so
- quoted diff headers are tokenized and extracted correctly,
- /dev/null headers are ignored before prefix stripping to avoid bogus
dev/null paths, and
- git apply output paths are unescaped from C-style quoting.
**Why**
This prevents potentially missed staging and misclassified paths when
applying or reverting patches, which could lead to incorrect behavior
for repos with spaces or escaped characters in filenames.
**Impact**
I checked and this is only used in the cloud tasks support and `codex
apply <task_id>` flow.
