feat: 考核系统升级 P0+P1+P2 — 体验/题库/配置增强

P0 — 答题体验优化:
- 题序导航点：题目进度可视化，标记题目标记
- 标记回头检查: 点击🏷️按钮标记当前题，导航点变黄色
- 提交确认弹窗: 未答完时提交弹出确认对话框

P1 — 题库管理增强:
- QuestionBankItem 新增 tags 字段（多标签过滤）
- 新增 question_bank_templates 联表（题库跨模板复用）

P2 — 考试配置增强:
- AssessmentTemplate 新增字段:
  - attemptLimit (尝试次数限制)
  - scheduledStart/scheduledEnd (预约时段)
  - reviewMode (回顾模式: none/after_completion/per_question)
  - shuffleQuestions (每题随机排序)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/assessment/entities/question-bank-item.entity.ts

@@ -92,6 +92,10 @@ export class QuestionBankItem {
   @Column({ type: 'simple-json', nullable: true, name: 'followup_hints' })
   followupHints: string[] | null;
 
+  /** P1: Tags for cross-category filtering */
+  @Column({ type: 'simple-json', nullable: true })
+  tags: string[] | null;
+
   @Column({ name: 'created_by', nullable: true, type: 'text' })
   createdBy: string | null;