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/template_prompt.go

@@ -30,6 +30,9 @@ func buildGenerationPrompt(
 	if contextBlock != "" {
 		sections = append(sections, prompts.PromptContextSection(contextBlock))
 	}
+	if brandPrompt := RenderBrandPromptContext(extractBrandPromptContext(params)); brandPrompt != "" {
+		sections = append(sections, brandPrompt)
+	}
 
 	if strings.TrimSpace(knowledgePrompt) != "" {
 		sections = append(sections, knowledgePrompt)