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/supplemental_test.go

@@ -173,13 +173,15 @@ func TestDecodeMessage_UserWithOnlyToolResults(t *testing.T) {
 }
 
 func TestDecodeContentBlocks_Nil(t *testing.T) {
-	blocks := decodeContentBlocks(nil)
+	blocks, err := decodeContentBlocks(nil)
+	require.NoError(t, err)
 	assert.Len(t, blocks, 1)
 	assert.Equal(t, "", blocks[0].Text)
 }
 
 func TestDecodeContentBlocks_String(t *testing.T) {
-	blocks := decodeContentBlocks("hello")
+	blocks, err := decodeContentBlocks("hello")
+	require.NoError(t, err)
 	assert.Len(t, blocks, 1)
 	assert.Equal(t, "hello", blocks[0].Text)
 }
@@ -217,8 +219,10 @@ func TestEncodeToolChoice(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			result := encodeToolChoice(tt.choice)
-			assert.Equal(t, tt.want["type"], result.(map[string]any)["type"])
-			assert.Equal(t, tt.want["name"], result.(map[string]any)["name"])
+			r, ok := result.(map[string]any)
+			require.True(t, ok)
+			assert.Equal(t, tt.want["type"], r["type"])
+			assert.Equal(t, tt.want["name"], r["name"])
 		})
 	}
 }
@@ -315,12 +319,15 @@ func TestEncodeRequest_WithTools(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	tools := result["tools"].([]any)
+	tools, okt := result["tools"].([]any)
+	require.True(t, okt)
 	assert.Len(t, tools, 1)
-	tool := tools[0].(map[string]any)
+	tool, okt2 := tools[0].(map[string]any)
+	require.True(t, okt2)
 	assert.Equal(t, "search", tool["name"])
 	assert.Equal(t, "Search things", tool["description"])
-	tc := result["tool_choice"].(map[string]any)
+	tc, oktc := result["tool_choice"].(map[string]any)
+	require.True(t, oktc)
 	assert.Equal(t, "auto", tc["type"])
 }
 
@@ -354,9 +361,9 @@ func TestEncodeResponse_UsageWithCacheAndCreation(t *testing.T) {
 		Content:    []canonical.ContentBlock{canonical.NewTextBlock("ok")},
 		StopReason: &sr,
 		Usage: canonical.CanonicalUsage{
-			InputTokens:        100,
-			OutputTokens:       50,
-			CacheReadTokens:    &cacheRead,
+			InputTokens:         100,
+			OutputTokens:        50,
+			CacheReadTokens:     &cacheRead,
 			CacheCreationTokens: &cacheCreation,
 		},
 	}
@@ -366,7 +373,8 @@ func TestEncodeResponse_UsageWithCacheAndCreation(t *testing.T) {
 
 	var result map[string]any
 	require.NoError(t, json.Unmarshal(body, &result))
-	usage := result["usage"].(map[string]any)
+	usage, oku := result["usage"].(map[string]any)
+	require.True(t, oku)
 	assert.Equal(t, float64(100), usage["input_tokens"])
 	assert.Equal(t, float64(30), usage["cache_read_input_tokens"])
 	assert.Equal(t, float64(10), usage["cache_creation_input_tokens"])