feat(tenant): inject brand description context into every generation path

Include the current brand description in template, custom, imitation,
and KOL article-generation prompts while bounding prompt growth.

- Add a shared brand-context builder that resolves the current brand,
  compacts long descriptions, and caps rendered output at 2000 runes.
- Snapshot a structured brand prompt context on queued tasks so old
  jobs stay reproducible and retries stay stable.
- Route brand-profile facts through the existing typed fact guard so
  founding dates and year counts get the same pre-persistence validation
  as RAG facts, with brand facts outranking conflicting RAG facts.
- Fix the KOL creator to attach the brand scope its worker consumes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/article_generation_payload.go

@@ -1,6 +1,10 @@
 package app
 
-import "github.com/geo-platform/tenant-api/internal/tenant/repository"
+import (
+	"encoding/json"
+
+	"github.com/geo-platform/tenant-api/internal/tenant/repository"
+)
 
 const (
 	generationPayloadTemplateKey            = "__snapshot_template_key"
@@ -13,6 +17,8 @@ const (
 	generationPayloadPromptRuleTone         = "__snapshot_prompt_rule_tone"
 	generationPayloadPromptRuleWordCount    = "__snapshot_prompt_rule_word_count"
 	generationPayloadKnowledgePrompt        = "__snapshot_knowledge_prompt"
+	generationPayloadKnowledgeFacts         = "__snapshot_knowledge_fact_constraints"
+	generationPayloadBrandPromptContext     = "__snapshot_brand_prompt_context"
 )
 
 func attachTemplateSnapshot(payload map[string]interface{}, record *repository.TemplateRecord) map[string]interface{} {
@@ -32,6 +38,65 @@ func attachTemplateSnapshot(payload map[string]interface{}, record *repository.T
 	return payload
 }
 
+func attachBrandPromptContext(payload map[string]interface{}, brandCtx *BrandPromptContext) map[string]interface{} {
+	if payload == nil {
+		payload = map[string]interface{}{}
+	}
+	if brandCtx == nil {
+		delete(payload, generationPayloadBrandPromptContext)
+		return payload
+	}
+	normalized := normalizeBrandPromptContext(*brandCtx)
+	payload[generationPayloadBrandPromptContext] = &normalized
+	return payload
+}
+
+func extractBrandPromptContext(payload map[string]interface{}) *BrandPromptContext {
+	if payload == nil || payload[generationPayloadBrandPromptContext] == nil {
+		return nil
+	}
+	encoded, err := json.Marshal(payload[generationPayloadBrandPromptContext])
+	if err != nil {
+		return nil
+	}
+	var brandCtx BrandPromptContext
+	if err := json.Unmarshal(encoded, &brandCtx); err != nil {
+		return nil
+	}
+	if brandCtx.BrandID <= 0 {
+		return nil
+	}
+	brandCtx = normalizeBrandPromptContext(brandCtx)
+	return &brandCtx
+}
+
+func attachKnowledgeFactConstraints(payload map[string]interface{}, constraints []KnowledgeFactConstraint) map[string]interface{} {
+	if payload == nil {
+		payload = map[string]interface{}{}
+	}
+	if len(constraints) == 0 {
+		delete(payload, generationPayloadKnowledgeFacts)
+		return payload
+	}
+	payload[generationPayloadKnowledgeFacts] = constraints
+	return payload
+}
+
+func extractKnowledgeFactConstraints(payload map[string]interface{}) []KnowledgeFactConstraint {
+	if payload == nil || payload[generationPayloadKnowledgeFacts] == nil {
+		return nil
+	}
+	encoded, err := json.Marshal(payload[generationPayloadKnowledgeFacts])
+	if err != nil {
+		return nil
+	}
+	var constraints []KnowledgeFactConstraint
+	if err := json.Unmarshal(encoded, &constraints); err != nil {
+		return nil
+	}
+	return constraints
+}
+
 func extractTemplateSnapshot(payload map[string]interface{}) (string, string, *string) {
 	templateKey := extractString(payload, generationPayloadTemplateKey)
 	templateName := extractString(payload, generationPayloadTemplateName)