feat(kol): add SSE streaming for prompt assist

- Extract assist runtime (prompt building, response parsing, finalize)
  from the worker into kol_assist_runtime so the sync streaming path
  and the async task path share the same logic.
- Add POST /kol/manage/assist/stream as a Server-Sent Events endpoint
  emitting start/delta/completed/error events, and wire it to a
  streamAssist helper on kolManageApi that reports ApiClientError with
  the server's error envelope.
- Stream generated content live in KolPromptEditor and KolGenerateView,
  switching KolPromptEditArea to a boolean aiBusy flag and refining the
  generator page layout.
- Add KolAssistStreamEvent to shared types.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/kol_assist_runtime_test.go

@@ -0,0 +1,81 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFinalizeKolAssistResultRepairsDuplicateVariableIDs(t *testing.T) {
+	t.Parallel()
+
+	result, err := FinalizeKolAssistResult(
+		AssistRequest{Mode: kolAssistModeGenerate},
+		&KolAssistResult{
+			Content: "围绕 {{城市}} 和 {{目标词}} 输出内容",
+			Schema: KolSchemaJSON{
+				Variables: []KolVariableDefinition{
+					{ID: "var_dup", Key: "城市", Label: "城市", Type: KolVariableTypeInput, Required: true},
+					{ID: "var_dup", Key: "目标词", Label: "目标词", Type: KolVariableTypeInput, Required: true},
+				},
+			},
+		},
+	)
+
+	require.NoError(t, err)
+	require.Len(t, result.Schema.Variables, 2)
+	require.NotEqual(t, result.Schema.Variables[0].ID, result.Schema.Variables[1].ID)
+	require.Equal(t, "城市", result.Schema.Variables[0].Key)
+	require.Equal(t, "目标词", result.Schema.Variables[1].Key)
+}
+
+func TestFinalizeKolAssistResultOptimizePreservesExistingSchemaByKey(t *testing.T) {
+	t.Parallel()
+
+	originalMaxLength := 80
+
+	result, err := FinalizeKolAssistResult(
+		AssistRequest{
+			Mode: kolAssistModeOptimize,
+			Schema: &KolSchemaJSON{
+				Variables: []KolVariableDefinition{
+					{ID: "var_city", Key: "城市", Label: "城市", Type: KolVariableTypeInput, Required: true, MaxLength: intPtr(originalMaxLength)},
+				},
+			},
+		},
+		&KolAssistResult{
+			Content: "围绕 {{城市}} 优化提示词",
+			Schema: KolSchemaJSON{
+				Variables: []KolVariableDefinition{
+					{ID: "var_dup", Key: "城市", Label: "城市", Type: KolVariableTypeTextarea, Required: false},
+				},
+			},
+		},
+	)
+
+	require.NoError(t, err)
+	require.Len(t, result.Schema.Variables, 1)
+	require.Equal(t, "var_city", result.Schema.Variables[0].ID)
+	require.Equal(t, KolVariableTypeInput, result.Schema.Variables[0].Type)
+	require.NotNil(t, result.Schema.Variables[0].MaxLength)
+	require.Equal(t, originalMaxLength, *result.Schema.Variables[0].MaxLength)
+}
+
+func TestParseKolAssistResponseSupportsStringVariables(t *testing.T) {
+	t.Parallel()
+
+	result, err := ParseKolAssistResponse(`{"content":"围绕 {{城市}} 写内容","schema":{"variables":["城市"]}}`)
+
+	require.NoError(t, err)
+	require.Equal(t, "围绕 {{城市}} 写内容", result.Content)
+	require.Len(t, result.Schema.Variables, 1)
+	require.Equal(t, "城市", result.Schema.Variables[0].Key)
+}
+
+func TestExtractKolAssistContentFromPartialJSON(t *testing.T) {
+	t.Parallel()
+
+	content := extractKolAssistContentFromPartialJSON("{\"content\":\"第一段\\n第二")
+
+	require.Equal(t, "第一段\n第二", content)
+}