refactor(diff): improve security and stability of config change detection

Introduce formatProxyURL helper to sanitize proxy addresses before
logging, stripping credentials and path components while preserving
host information. Rework model hash computation to sort and deduplicate
name/alias pairs with case normalization, ensuring consistent output
regardless of input ordering. Add signature-based identification for
anonymous OpenAI-compatible provider entries to maintain stable keys
across configuration reloads. Replace direct stdout prints with
structured logger calls for file change notifications.

internal/watcher/diff/openai_compat.go

@@ -1,6 +1,8 @@
 package diff
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"sort"
 	"strings"
@@ -120,5 +122,62 @@ func openAICompatKey(entry config.OpenAICompatibility, index int) (string, strin
 			return "alias:" + alias, alias
 		}
 	}
-	return fmt.Sprintf("index:%d", index), fmt.Sprintf("entry-%d", index+1)
+	sig := openAICompatSignature(entry)
+	if sig == "" {
+		return fmt.Sprintf("index:%d", index), fmt.Sprintf("entry-%d", index+1)
+	}
+	short := sig
+	if len(short) > 8 {
+		short = short[:8]
+	}
+	return "sig:" + sig, "compat-" + short
+}
+
+func openAICompatSignature(entry config.OpenAICompatibility) string {
+	var parts []string
+
+	if v := strings.TrimSpace(entry.Name); v != "" {
+		parts = append(parts, "name="+strings.ToLower(v))
+	}
+	if v := strings.TrimSpace(entry.BaseURL); v != "" {
+		parts = append(parts, "base="+v)
+	}
+
+	models := make([]string, 0, len(entry.Models))
+	for _, model := range entry.Models {
+		name := strings.TrimSpace(model.Name)
+		alias := strings.TrimSpace(model.Alias)
+		if name == "" && alias == "" {
+			continue
+		}
+		models = append(models, strings.ToLower(name)+"|"+strings.ToLower(alias))
+	}
+	if len(models) > 0 {
+		sort.Strings(models)
+		parts = append(parts, "models="+strings.Join(models, ","))
+	}
+
+	if len(entry.Headers) > 0 {
+		keys := make([]string, 0, len(entry.Headers))
+		for k := range entry.Headers {
+			if trimmed := strings.TrimSpace(k); trimmed != "" {
+				keys = append(keys, strings.ToLower(trimmed))
+			}
+		}
+		if len(keys) > 0 {
+			sort.Strings(keys)
+			parts = append(parts, "headers="+strings.Join(keys, ","))
+		}
+	}
+
+	// Intentionally exclude API key material; only count non-empty entries.
+	if count := countAPIKeys(entry); count > 0 {
+		parts = append(parts, fmt.Sprintf("api_keys=%d", count))
+	}
+
+	if len(parts) == 0 {
+		return ""
+	}
+	sum := sha256.Sum256([]byte(strings.Join(parts, "|")))
+	return hex.EncodeToString(sum[:])
 }