gate: subagent guard allows a backslash-escaped letter inside git or its subcommand (g\it stash, git re\set) #317

Found by the #306 differential fuzz (43 of its 46 remaining false-allows; pre-existing, not caused by #306).

In a shell a backslash before an ordinary letter is dropped, so an escaped letter inside the git word or the subcommand still runs plain stash, reset or clean. The guard's anchor only strips one leading backslash, and the quote mask keeps backslash pairs as they are, so the subagent guard allows these. Fix direction: drop a backslash that precedes a non-special character when matching command and subcommand words, then fuzz it per docs/reference/repo-gotchas.md. Check irrecoverable.py for the same gap.