refactor: 压平数据模型 — 版本为执行主线，需求降为语义标签

核心改动：
- TestCase 主归属 versionId，requirementId 改为可选语义标签
- Bug 新增 versionId（直接挂版本）+ requirementId（可选追溯）
- 新增 calcVersionExecutionStatus() 版本执行态推导函数
  规则：DevTask全部提测→已提测，TestCase全部通过+Bug全关→可发布
- 概览页展示推导出的执行态标签
- BugTab 改为直接 versionId 查询（不再走 testCase→req 链路）
- 统计卡片"参与人员"替换为"未关闭Bug"

心智模型：
  版本（执行线）→ DevTask/TestCase/Bug
  需求（语义线）→ 解释为什么做，不驱动流程

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/stores/useBugStore.ts

@@ -25,6 +25,7 @@ interface BugState {
   deleteBug: (id: string) => void;
   changeStatus: (id: string, to: BugStatus, extra?: { resolution?: string }) => { ok: boolean; message?: string };
   getByTestCase: (caseId: string) => Bug[];
+  getByVersion: (versionId: string) => Bug[];
   getByAssignee: (assigneeId: string) => Bug[];
 }
 
@@ -86,6 +87,10 @@ export const useBugStore = create<BugState>((set, get) => ({
     return get().bugs.filter((b) => b.testCaseId === caseId);
   },
 
+  getByVersion: (versionId) => {
+    return get().bugs.filter((b) => b.versionId === versionId);
+  },
+
   getByAssignee: (assigneeId) => {
     return get().bugs.filter((b) => b.assigneeId === assigneeId);
   },

apps/web/stores/useTestCaseStore.ts

@@ -25,6 +25,7 @@ interface TestCaseState {
   deleteTestCase: (id: string) => void;
   changeStatus: (id: string, to: TestCaseStatus, extra?: { failReason?: string; blockReason?: string }) => { ok: boolean; message?: string };
   getByRequirement: (reqId: string) => TestCase[];
+  getByVersion: (versionId: string) => TestCase[];
   getByAssignee: (assigneeId: string) => TestCase[];
 }
 
@@ -89,6 +90,10 @@ export const useTestCaseStore = create<TestCaseState>((set, get) => ({
     return get().testCases.filter((c) => c.requirementId === reqId);
   },
 
+  getByVersion: (versionId) => {
+    return get().testCases.filter((c) => c.versionId === versionId);
+  },
+
   getByAssignee: (assigneeId) => {
     return get().testCases.filter((c) => c.assigneeId === assigneeId);
   },