chore: ruff auto-fix C401, C416, C408, PLR1722 (#23940)

C401:   set(x for x in y) -> {x for x in y}      (set comprehension)
C416:   [(k,v) for k,v in d] -> list(d.items())  (unnecessary listcomp)
C408:   tuple()/dict() -> ()/{}                   (unnecessary collection call)
PLR1722: exit() -> sys.exit()                     (adds import sys where needed)

21 instances fixed, 0 remaining. 19 files, +40/-36.

tools/web_tools.py

@@ -100,6 +100,7 @@ from tools.managed_tool_gateway import (
 from tools.tool_backend_helpers import managed_nous_tools_enabled, prefers_gateway
 from tools.url_safety import is_safe_url
 from tools.website_policy import check_website_access
+import sys
 
 logger = logging.getLogger(__name__)
 
@@ -2153,7 +2154,7 @@ if __name__ == "__main__":
         print(f"✅ Auxiliary model available: {default_summarizer_model}")
 
     if not web_available:
-        exit(1)
+        sys.exit(1)
 
     print("🛠️  Web tools ready for use!")