Refresh L7 control plane after runtime mutations

[kacy]

Summary

• add a shared L7 control-plane refresh helper for proxy route materialization and VIP steering
• call it after service API endpoint mutations, health registration, reconciler audit repairs, stale-endpoint quarantine, and node loss/recovery
• add regressions for endpoint drain/delete and node-loss route count refresh

Validation

• zig fmt on touched files
• single-process targeted zig build test runs for:
  • route handles POST drain and DELETE endpoint
  • node loss refreshes l7 proxy route counts
• single-process timeout 60 zig build test -Doptimize=ReleaseSafe
• the focused and broad builds timed out without emitted failures

Commit

• Refresh L7 control plane after runtime mutations