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/kol_generation_payload_test.go

@@ -0,0 +1,21 @@
+package app
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestAttachKolGenerationKnowledgeScopeMatchesWorkerContract(t *testing.T) {
+	taskInput := map[string]any{
+		"rendered_prompt": "write an article",
+	}
+
+	attachKolGenerationKnowledgeScope(taskInput, 4, []int64{47, 17, 47, 0})
+
+	if got := int64(extractInt(taskInput, "brand_id")); got != 4 {
+		t.Fatalf("worker brand_id = %d, want 4", got)
+	}
+	if got := extractKnowledgeGroupIDs(taskInput["knowledge_group_ids"]); !reflect.DeepEqual(got, []int64{17, 47}) {
+		t.Fatalf("worker knowledge_group_ids = %#v, want [17 47]", got)
+	}
+}