feat(imitation): simplify form fields and make brand_name required

Remove industry, target_audience, content_goal, tone, and length_goal from the imitation form; brand_name is now mandatory with autocomplete from brand library, keywords are pre-populated from the selected brand's search keywords, and output length is hardcoded to ~2000 characters in the prompt.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/article_imitation_service.go

@@ -47,13 +47,8 @@ type GenerateImitationRequest struct {
 	SourceURL         string   `json:"source_url" binding:"required"`
 	SourceTitle       string   `json:"source_title"`
 	Locale            string   `json:"locale"`
-	Industry          string   `json:"industry"`
 	BrandName         string   `json:"brand_name"`
 	Region            string   `json:"region"`
-	TargetAudience    string   `json:"target_audience"`
-	ContentGoal       string   `json:"content_goal"`
-	Tone              string   `json:"tone"`
-	LengthGoal        string   `json:"length_goal"`
 	Keywords          []string `json:"keywords"`
 	PreservePoints    string   `json:"preserve_points"`
 	AvoidPoints       string   `json:"avoid_points"`
@@ -135,6 +130,9 @@ func (s *ArticleImitationService) Generate(ctx context.Context, req GenerateImit
 	if err != nil {
 		return nil, err
 	}
+	if strings.TrimSpace(req.BrandName) == "" {
+		return nil, response.ErrBadRequest(40001, "brand_name_required", "brand_name is required")
+	}
 
 	quotaRepo := repository.NewQuotaRepository(s.pool)
 	balance, err := quotaRepo.GetCurrentBalance(ctx, actor.TenantID, "article_generation")
@@ -587,13 +585,9 @@ func buildImitationInputParams(sourceURL string, req GenerateImitationRequest) m
 		"source_url":          sourceURL,
 		"source_title":        strings.TrimSpace(req.SourceTitle),
 		"locale":              normalizeImitationLocale(req.Locale),
-		"industry":            strings.TrimSpace(req.Industry),
 		"brand_name":          strings.TrimSpace(req.BrandName),
 		"region":              strings.TrimSpace(req.Region),
-		"target_audience":     strings.TrimSpace(req.TargetAudience),
-		"content_goal":        strings.TrimSpace(req.ContentGoal),
-		"tone":                strings.TrimSpace(req.Tone),
-		"length_goal":         strings.TrimSpace(req.LengthGoal),
+		"length_goal":         "2000字左右",
 		"keywords":            normalizeImitationKeywords(req.Keywords),
 		"preserve_points":     strings.TrimSpace(req.PreservePoints),
 		"avoid_points":        strings.TrimSpace(req.AvoidPoints),
@@ -631,12 +625,8 @@ func buildImitationGenerationPrompt(params map[string]interface{}, sourceContent
 	}
 
 	var settings strings.Builder
-	appendPromptLine(&settings, "industry", extractString(params, "industry"))
 	appendPromptLine(&settings, "brand_name", extractString(params, "brand_name"))
 	appendPromptLine(&settings, "region", extractString(params, "region"))
-	appendPromptLine(&settings, "target_audience", extractString(params, "target_audience"))
-	appendPromptLine(&settings, "content_goal", extractString(params, "content_goal"))
-	appendPromptLine(&settings, "tone", extractString(params, "tone"))
 	appendPromptLine(&settings, "length_goal", extractString(params, "length_goal"))
 	if len(keywords) > 0 {
 		appendPromptLine(&settings, "keywords", strings.Join(keywords, "、"))
@@ -674,12 +664,8 @@ func buildImitationKnowledgeQuery(params map[string]interface{}) string {
 	}
 
 	appendValue(extractString(params, "source_title"))
-	appendValue(extractString(params, "industry"))
 	appendValue(extractString(params, "brand_name"))
 	appendValue(extractString(params, "region"))
-	appendValue(extractString(params, "target_audience"))
-	appendValue(extractString(params, "content_goal"))
-	appendValue(extractString(params, "tone"))
 	appendValue(strings.Join(extractStringList(params["keywords"], 16), "\n"))
 	appendValue(extractString(params, "extra_requirements"))