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/openai/encoder_test.go

@@ -45,9 +45,11 @@ func TestEncodeRequest_SystemInjection(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, 2)
-	firstMsg := msgs[0].(map[string]any)
+	firstMsg, ok := msgs[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "system", firstMsg["role"])
 	assert.Equal(t, "你是助手", firstMsg["content"])
 }
@@ -72,12 +74,15 @@ func TestEncodeRequest_ToolCalls(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	msgs := result["messages"].([]any)
-	assistantMsg := msgs[0].(map[string]any)
+	msgs, ok := result["messages"].([]any)
+	require.True(t, ok)
+	assistantMsg, ok := msgs[0].(map[string]any)
+	require.True(t, ok)
 	toolCalls, ok := assistantMsg["tool_calls"].([]any)
 	require.True(t, ok)
 	assert.Len(t, toolCalls, 1)
-	tc := toolCalls[0].(map[string]any)
+	tc, ok := toolCalls[0].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "call_1", tc["id"])
 }
 
@@ -100,11 +105,11 @@ func TestEncodeRequest_Thinking(t *testing.T) {
 func TestEncodeResponse_Basic(t *testing.T) {
 	sr := canonical.StopReasonEndTurn
 	resp := &canonical.CanonicalResponse{
-		ID:      "resp-1",
-		Model:   "gpt-4",
-		Content: []canonical.ContentBlock{canonical.NewTextBlock("你好")},
+		ID:         "resp-1",
+		Model:      "gpt-4",
+		Content:    []canonical.ContentBlock{canonical.NewTextBlock("你好")},
 		StopReason: &sr,
-		Usage:   canonical.CanonicalUsage{InputTokens: 10, OutputTokens: 5},
+		Usage:      canonical.CanonicalUsage{InputTokens: 10, OutputTokens: 5},
 	}
 
 	body, err := encodeResponse(resp)
@@ -115,9 +120,12 @@ func TestEncodeResponse_Basic(t *testing.T) {
 	assert.Equal(t, "resp-1", result["id"])
 	assert.Equal(t, "chat.completion", result["object"])
 
-	choices := result["choices"].([]any)
-	choice := choices[0].(map[string]any)
-	msg := choice["message"].(map[string]any)
+	choices, ok := result["choices"].([]any)
+	require.True(t, ok)
+	choice, ok := choices[0].(map[string]any)
+	require.True(t, ok)
+	msg, ok := choice["message"].(map[string]any)
+	require.True(t, ok)
 	assert.Equal(t, "你好", msg["content"])
 	assert.Equal(t, "stop", choice["finish_reason"])
 }
@@ -126,9 +134,9 @@ func TestEncodeResponse_ToolUse(t *testing.T) {
 	sr := canonical.StopReasonToolUse
 	input := json.RawMessage(`{"q":"test"}`)
 	resp := &canonical.CanonicalResponse{
-		ID:      "resp-2",
-		Model:   "gpt-4",
-		Content: []canonical.ContentBlock{canonical.NewToolUseBlock("call_1", "search", input)},
+		ID:         "resp-2",
+		Model:      "gpt-4",
+		Content:    []canonical.ContentBlock{canonical.NewToolUseBlock("call_1", "search", input)},
 		StopReason: &sr,
 	}
 
@@ -137,8 +145,12 @@ func TestEncodeResponse_ToolUse(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	choices := result["choices"].([]any)
-	msg := choices[0].(map[string]any)["message"].(map[string]any)
+	choices, okc := result["choices"].([]any)
+	require.True(t, okc)
+	msgMap, okm := choices[0].(map[string]any)
+	require.True(t, okm)
+	msg, okmsg := msgMap["message"].(map[string]any)
+	require.True(t, okmsg)
 	tcs, ok := msg["tool_calls"].([]any)
 	require.True(t, ok)
 	assert.Len(t, tcs, 1)
@@ -158,7 +170,8 @@ func TestEncodeModelsResponse(t *testing.T) {
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
 	assert.Equal(t, "list", result["object"])
-	data := result["data"].([]any)
+	data, okd := result["data"].([]any)
+	require.True(t, okd)
 	assert.Len(t, data, 2)
 }
 
@@ -317,8 +330,12 @@ func TestEncodeResponse_Thinking(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	choices := result["choices"].([]any)
-	msg := choices[0].(map[string]any)["message"].(map[string]any)
+	choices, okch := result["choices"].([]any)
+	require.True(t, okch)
+	msgMap, okmm := choices[0].(map[string]any)
+	require.True(t, okmm)
+	msg, okmsg := msgMap["message"].(map[string]any)
+	require.True(t, okmsg)
 	assert.Equal(t, "回答", msg["content"])
 	assert.Equal(t, "思考过程", msg["reasoning_content"])
 }