test(dms): cover sql workbench core flow Fixes #846

[actiontech-bot]

Fixes #846

Summary

• add focused tests for SQL workbench proxy configuration and route wiring
• extract shared SQL workbench access filtering and cover access flow cases
• keep runtime behavior unchanged while adding direct verification around core flow helpers

Validation

• make EDITION=ce docker_install
• targeted go test passed for ./internal/apiserver/service ./internal/dms/biz ./internal/sql_workbench/service
• repo-wide golangci-lint/go vet blocked by pre-existing failures in internal/dms/pkg/constant, internal/dms/pkg/errors, internal/dms/storage