fix(server): force C locale for git root lookup

Git translates its "not a git repository" diagnostic, so non-English
hosts would miss the negative cache and respawn git on every resolve.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WvDgDwRRG8xvtoABQ8KwtC
9ba1cb5085Claude committed on 9/25/2026, 11:47:35 PMparent8ddd79e
1 file changedLine totals unavailable