feat(keywords): rename brand-question terminology to search-keyword + add entity exclusion

- Rename UI/prompt labels: "品牌主问题" → "优化关键词", "搜索问题" → "搜索词"
- Add brand/competitor entity exclusion filter in question expansion (AI distill path)
- Refactor combination question text normalization, remove manual question-mark appending
- Update prompts to emphasize commercial-intent search queries over editorial phrasing
- Sync prompt changes across server/configs, deploy, and k3s configs
- Update i18n, frontend views (BrandQuestionCreate, TemplateWizard), and test fixtures

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

server/internal/tenant/app/template_prompt_test.go

@@ -20,7 +20,7 @@ func TestBuildPromptContextUsesChineseLabels(t *testing.T) {
 		"- 语言: zh-CN",
 		"- 标题: 测试标题",
 		"- 品牌名: Rankly",
-			"- 品牌主问题: GEO 排名",
+		"- 优化关键词: GEO 排名",
 		"- 已选段落: 引言 > 结论",
 	} {
 		if !strings.Contains(context, expected) {