fix(phase-2): add thread-safety to ModelRegistry and Router reload operations

internal/models/registry.go

@@ -1,6 +1,9 @@
 package models
 
-import "strings"
+import (
+	"strings"
+	"sync"
+)
 
 // CanonicalProviders lists the original model creators in priority order.
 // When a model name exists in multiple providers (e.g. deepseek-v4-pro in
@@ -22,6 +25,7 @@ var CanonicalProviders = []string{
 }
 
 type ModelRegistry struct {
+	mu        sync.RWMutex
 	Providers map[string]ProviderInfo `json:"-"`
 }
 
@@ -173,6 +177,12 @@ func (r *ModelRegistry) findAllForwardFuzzy(modelID string) (*ModelMetadata, boo
 // etc.) from overriding the original provider's authoritative pricing and
 // limits.
 func (r *ModelRegistry) FindModel(modelID string) *ModelMetadata {
+	if r == nil {
+		return nil
+	}
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	// 1. Exact key match — canonical first, then all
 	if m, ok := r.findInCanonical(modelID); ok {
 		return m