feat: 接入分镜单集重生成接口

接入后端正式单集 Storyboard Shot 重生成能力，补齐校验回执、旧 Shot 缓存失效与页面刷新逻辑。

tests/lib/http.test.ts

@@ -46,9 +46,11 @@ describe('后端 API 契约', () => {
     it('分镜只调用正式项目接口，并保持 force 和零次修复参数', async () => {
         const fetcher = vi.fn<typeof fetch>().mockImplementation(async () => new Response('{"data":{}}'))
         vi.stubGlobal('fetch', fetcher)
+        await storyboardApi.regenerateEpisodeShots('a/b', 3)
         await storyboardApi.generateDirections('a/b', { concurrency: 2, force: false })
         await storyboardApi.generateVisualStates('p', { concurrency: 3, force: true, maxRepairAttempts: 0 })
         expect(fetcher.mock.calls.map(([url, init]) => [url, init?.method, JSON.parse(init!.body as string)])).toEqual([
+            ['/api/projects/a%2Fb/storyboard-shots/regenerate', 'POST', { episodeNo: 3 }],
             ['/api/projects/a%2Fb/storyboard-directions/generate', 'POST', { concurrency: 2, force: false }],
             [
                 '/api/projects/p/storyboard-visual-states/generate',