feat: 配置 golangci-lint 静态分析并修复存量违规

- 新增 backend/.golangci.yml 配置 12 个 linter（forbidigo、errorlint、errcheck、staticcheck、revive、gocritic、gosec、bodyclose、noctx、nilerr、goimports、gocyclo）
- 新增 lefthook.yml 配置 pre-commit hook 自动运行 lint
- 修复存量代码违规：errors.Is/As 替换、zap.Error 替换、import 排序、errcheck 修复
- 更新 README 补充编码规范说明
- 归档 backend-code-lint 变更

backend/internal/conversion/anthropic/encoder_test.go

@@ -33,7 +33,8 @@ func TestEncodeRequest_Basic(t *testing.T) {
 	assert.Equal(t, true, result["stream"])
 	assert.Equal(t, float64(1024), result["max_tokens"])
 
-	msgs := result["messages"].([]any)
+	msgs, ok := result["messages"].([]any)
+	require.True(t, ok)
 	assert.Len(t, msgs, 1)
 }
 
@@ -55,17 +56,20 @@ func TestEncodeRequest_ToolMergeIntoUser(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	msgs := result["messages"].([]any)
+	msgs, ok := result["messages"].([]any)
+	require.True(t, ok)
 
 	// tool 消息应被合并到相邻 user 消息
 	foundToolResult := false
 	for _, m := range msgs {
-		msgMap := m.(map[string]any)
+		msgMap, ok := m.(map[string]any)
+		require.True(t, ok)
 		if msgMap["role"] == "user" {
 			content, ok := msgMap["content"].([]any)
 			if ok {
 				for _, c := range content {
-					block := c.(map[string]any)
+					block, ok := c.(map[string]any)
+					require.True(t, ok)
 					if block["type"] == "tool_result" {
 						foundToolResult = true
 					}
@@ -93,8 +97,10 @@ func TestEncodeRequest_FirstUserGuarantee(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	msgs := result["messages"].([]any)
-	firstMsg := msgs[0].(map[string]any)
+	msgs, ok := result["messages"].([]any)
+	require.True(t, ok)
+	firstMsg, ok := msgs[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "user", firstMsg["role"])
 }
 
@@ -140,9 +146,11 @@ func TestEncodeResponse_Basic(t *testing.T) {
 	assert.Equal(t, "assistant", result["role"])
 	assert.Equal(t, "end_turn", result["stop_reason"])
 
-	content := result["content"].([]any)
+	content, ok := result["content"].([]any)
+	require.True(t, ok)
 	assert.Len(t, content, 1)
-	block := content[0].(map[string]any)
+	block, ok := content[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "text", block["type"])
 	assert.Equal(t, "你好", block["text"])
 }
@@ -160,10 +168,12 @@ func TestEncodeModelsResponse(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	data := result["data"].([]any)
+	data, ok := result["data"].([]any)
+	require.True(t, ok)
 	assert.Len(t, data, 1)
 
-	model := data[0].(map[string]any)
+	model, ok := data[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "claude-3-opus", model["id"])
 	// created 应为 RFC3339 格式
 	createdAt, ok := model["created_at"].(string)
@@ -280,11 +290,14 @@ func TestEncodeRequest_ConsecutiveRoleMerge(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	msgs := result["messages"].([]any)
+	msgs, ok := result["messages"].([]any)
+	require.True(t, ok)
 	assert.Len(t, msgs, 1)
-	userMsg := msgs[0].(map[string]any)
+	userMsg, ok := msgs[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "user", userMsg["role"])
-	content := userMsg["content"].([]any)
+	content, ok := userMsg["content"].([]any)
+	require.True(t, ok)
 	assert.Len(t, content, 2)
 }
 
@@ -321,7 +334,8 @@ func TestEncodeResponse_ReasoningTokens(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	usage := result["usage"].(map[string]any)
+	usage, ok := result["usage"].(map[string]any)
+	require.True(t, ok)
 	_, hasReasoning := usage["reasoning_tokens"]
 	assert.False(t, hasReasoning)
 }
@@ -341,9 +355,11 @@ func TestEncodeResponse_ToolUse(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	content := result["content"].([]any)
+	content, ok := result["content"].([]any)
+	require.True(t, ok)
 	assert.Len(t, content, 1)
-	block := content[0].(map[string]any)
+	block, ok := content[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "tool_use", block["type"])
 	assert.Equal(t, "tool_1", block["id"])
 	assert.Equal(t, "search", block["name"])