Fix Python 3.11 compatibility in api_import.py

Extract backslash-containing .replace() calls out of f-string expressions
to fix SyntaxError on Python <3.12 where f-string expression parts cannot
include backslashes.

https://claude.ai/code/session_01VzBz78XPLwNAzDDaSFsTbC

Author: claude

local_nexus_controller/routers/api_import.py

@@ -1033,9 +1033,11 @@ def github_localize_pr(req: GitHubLocalizePrRequest) -> dict:
         if not str(svc.get("working_directory") or "").strip():
             svc["working_directory"] = "{REPO_ROOT}"
         if not str(svc.get("start_command") or "").strip():
-            svc["start_command"] = f"powershell -ExecutionPolicy Bypass -File {start_ps1_path.replace('/', '\\\\')}"
+            _start_win = start_ps1_path.replace('/', '\\')
+            svc["start_command"] = f"powershell -ExecutionPolicy Bypass -File {_start_win}"
         if not str(svc.get("stop_command") or "").strip():
-            svc["stop_command"] = f"powershell -ExecutionPolicy Bypass -File {stop_ps1_path.replace('/', '\\\\')}"
+            _stop_win = stop_ps1_path.replace('/', '\\')
+            svc["stop_command"] = f"powershell -ExecutionPolicy Bypass -File {_stop_win}"
 
         tech = svc.get("tech_stack")
         if not isinstance(tech, list):