fix: correct settings.json filename and bump version to v5.2.8

- Fix incorrect filename reference from setting.json to settings.json in backend.go
- Update corresponding test fixtures to use correct filename
- Bump version from 5.2.7 to 5.2.8

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/main.go

@@ -14,7 +14,7 @@ import (
 )
 
 const (
-	version             = "5.2.7"
+	version             = "5.2.8"
 	defaultWorkdir      = "."
 	defaultTimeout      = 7200 // seconds (2 hours)
 	codexLogLineLimit   = 1000