feat(embed,ui04): E01 v2 contract skeleton — displayMode/scrollSpeed/reactionsEnabled, v2 loader entry and fixed 195x280 shell

- contracts: EmbedSlotSettings optional v2 fields (carousel default) + SlotSettingsPayload; gen + redocly green
- api: DTO validation + normalization full-set (cn manage + ov public projection share normalizeStoredSettings)
- embed-loader: params v2 parse/merge/url family, loader-v2.js fixed shell (border/radius/#10161E/safe-area, resize ignored, stack gap 12), dual-artifact build+sync; v1 source frozen
- viewer: EmbedPage v=2 branch, EmbedStream (viewport/track/real anchors/collapse/empty), stream.ts pure fns, i18n zh/en
- admin: types + utils (create default vertical-stream, clampScrollSpeed, v1/v2 snippet selection)
- tests: loader 36 (+9 v2), viewer 222, admin 82, api unit 51, v1 embed e2e 20, v2 E01 gate 2 (195x280 desktop+mobile cross-origin, no footer)

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

apps/viewer/src/i18n/locales/en.ts

@@ -33,6 +33,9 @@ export default {
     play: 'Play carousel',
     prev: 'Previous photo',
     next: 'Next photo',
+    // UI-04 v2 vertical photo stream window
+    streamLabel: 'Event photo window',
+    collapseWindow: 'Collapse photo window',
   },
   download: {
     action: 'Download photo',

apps/viewer/src/i18n/locales/zh-CN.ts

@@ -34,6 +34,9 @@ export default {
     play: '播放轮播',
     prev: '上一张',
     next: '下一张',
+    // —— UI-04 v2 垂直照片流窗 ——
+    streamLabel: '活动照片窗',
+    collapseWindow: '收起照片窗',
   },
   download: {
     action: '下载图片',