refactor(watcher): extract config diff helpers

Break out config diffing, hashing, and OpenAI compatibility utilities into a dedicated diff package, update watcher to consume them, and add comprehensive tests for diff logic and watcher behavior.

internal/watcher/diff/model_hash.go

@@ -0,0 +1,62 @@
+package diff
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"sort"
+	"strings"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+)
+
+// ComputeOpenAICompatModelsHash returns a stable hash for OpenAI-compat models.
+// Used to detect model list changes during hot reload.
+func ComputeOpenAICompatModelsHash(models []config.OpenAICompatibilityModel) string {
+	if len(models) == 0 {
+		return ""
+	}
+	data, _ := json.Marshal(models)
+	sum := sha256.Sum256(data)
+	return hex.EncodeToString(sum[:])
+}
+
+// ComputeVertexCompatModelsHash returns a stable hash for Vertex-compatible models.
+func ComputeVertexCompatModelsHash(models []config.VertexCompatModel) string {
+	if len(models) == 0 {
+		return ""
+	}
+	data, _ := json.Marshal(models)
+	sum := sha256.Sum256(data)
+	return hex.EncodeToString(sum[:])
+}
+
+// ComputeClaudeModelsHash returns a stable hash for Claude model aliases.
+func ComputeClaudeModelsHash(models []config.ClaudeModel) string {
+	if len(models) == 0 {
+		return ""
+	}
+	data, _ := json.Marshal(models)
+	sum := sha256.Sum256(data)
+	return hex.EncodeToString(sum[:])
+}
+
+// ComputeExcludedModelsHash returns a normalized hash for excluded model lists.
+func ComputeExcludedModelsHash(excluded []string) string {
+	if len(excluded) == 0 {
+		return ""
+	}
+	normalized := make([]string, 0, len(excluded))
+	for _, entry := range excluded {
+		if trimmed := strings.TrimSpace(entry); trimmed != "" {
+			normalized = append(normalized, strings.ToLower(trimmed))
+		}
+	}
+	if len(normalized) == 0 {
+		return ""
+	}
+	sort.Strings(normalized)
+	data, _ := json.Marshal(normalized)
+	sum := sha256.Sum256(data)
+	return hex.EncodeToString(sum[:])
+}