feat: integrate config system into relay main.go

Add support for loading configuration from YAML file via -config flag.
Wire up auth, rate limiting, and metrics interceptors based on config.

Changes:
- Add -config flag to relay command
- Use config types directly in auth package (AuthOperationConfig)
- Add conversion methods: RateLimitConfig.ToRateLimiter(), MetricsConfig.ToMetrics()
- Add Metrics.Serve() method for prometheus HTTP endpoint
- Update main.go to initialize interceptors from config
- Fix type naming: OperationAuthConfig -> AuthOperationConfig for consistency

Config now supports complete relay setup including auth read/write
allowlists, rate limiting, and prometheus metrics.

1 files changed, 9 insertions, 0 deletions

diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
index 3cb675f..9030d67 100644
--- a/internal/metrics/metrics.go
+++ b/internal/metrics/metrics.go
@@ -1,8 +1,11 @@
 package metrics
 
 import (
+        "net/http"
+
         "github.com/prometheus/client_golang/prometheus"
         "github.com/prometheus/client_golang/prometheus/promauto"
+        "github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 // Metrics holds all Prometheus metrics for the relay.
@@ -280,3 +283,9 @@ const (
         StatusRateLimited     RequestStatus = "rate_limited"
         StatusInvalidRequest  RequestStatus = "invalid_request"
 )
+
+func (m *Metrics) Serve(addr, path string) error {
+        mux := http.NewServeMux()
+        mux.Handle(path, promhttp.Handler())
+        return http.ListenAndServe(addr, mux)
+}