phsl / new-api

Summary
1. Consider “both unset” as identical
   • When both localValue and upstreamValue are nil, mark upstreamValue as "same" to avoid showing “Not set”.

2. Exclude fully-synced upstream channels from result
   • Scan `differences` to detect channels that contain at least one divergent value.
   • Remove channels whose every ratio is either `"same"` or `nil`, so the frontend only receives actionable discrepancies.

Why
These changes reduce visual noise in the Upstream Ratio Sync table, making it easier for admins to focus on models requiring attention. No functional regressions or breaking API changes are introduced.