docs: bilingual counterparts for the projection READMEs; review-driven RFC precision

New zh pairs for the session-projection group and package READMEs (both
gained their missing language-switcher lines); the packages/README rows,
apiproxy README, and tool-todo README zh sides catch up with their edited
English; the group README's stale ProjectionProvider name becomes
ProjectionDefinition. RFC precision from review: asOfSeq is the last
event's seq (session.seq - 1, -1 empty; subscribed.lastSeq vocabulary) and
a new risk names the accepted dev-only staleness window when registry
churn changes the key set mid-session. Pairing re-recorded; 540 pairs
consistent.

packages/todo/tool-todo/README.i18n.yaml

@@ -1,6 +1,6 @@
 # Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
-#   pnpm run verify-translation-pairing --write
-README.md: 3615f68953cfe6cdc0e6fc41bf75b8dfdf90a310
-README.zh.md: c4a7d829cc1583b65d2c8afa1683d957f68722e9
+#   pnpm run verify-translation-pairing --write packages/todo/tool-todo/README.md
+README.md: 5d748e981e8cc75a189916ab87e5d486ba916603
+README.zh.md: ddd22eb13fde81ddd05465ca789b302bb33bb8d9

packages/todo/tool-todo/README.zh.md

@@ -22,6 +22,10 @@
 
 规范结果为 `{ todos, counts: { pending, inProgress, completed } }`；其 Native 渲染器返回精简的更新确认。工具还会写入完整 `todo/write` 会话事件。UI 订阅事件流，并自行渲染该持久列表：[TUI 应用](../../examples/tui-demo)将其显示为持久计划，[web 客户端](../../client/ui-conversation)则基于 `ConversationSnapshot.todos` 渲染计划横条与专属工具行（[Agent Note](../../../.agents/notes/implemented/feature/2026-07-23-web-todo-display.md)）。
 
+## 会话投影
+
+当组合挂载了 `ctx.sessionProjections`（[`@deepseek-ai/dsh-session-projection`](../../session-projection/session-projection/README.md)）时，本包在一个注入式子插件下注册 `todos` 投影单元：`init` = `null`（尚无写入）、`apply` = 从每个 `todo/write` 取整表（last-wins；其余事件都返回同一个状态引用）、`view` = 恒等、`stateVersion` = 1。key 在本包合并进 `SessionProjectionMap`（经接口包的 `/types` 出口）；框架驱动该单元，载体在历史尾页与 `session/projection` 推送帧上供给该值。未装注册表的组合不受影响。
+
 ## 导出形状
 
 函数／命名空间插件：导出 `name`/`inject`/`apply`，不提供默认导出。意外的 `export default` 会通过 Loader 的 `unwrapExports` 折叠模块并丢弃 `inject`（参见 [docs/postmortem/0001](../../../docs/postmortem/0001-acp-default-export-drops-inject.md)）。