DSH: translate ACP events and one-shot interactions safely

## 目标

将公开 ACP events 与 one-shot permission 映射为有限、版本化的 Cindy contracts；未知数据绝不变成完成或授权。

## 交付

- `DshBridgeEnvelope`、capability snapshot 与 `cindy-dsh` activity contract。
- 精确的 text/thought/tool/usage/status/error/done mapping；unknown/stale/duplicate/cross-session 全部 fail closed。
- toolCallId 的 allow-once/reject-once/timeout/disconnect resolver。

## 验收

- raw runtime payload/secret 不跨 Renderer/Mobile。
- 乱序、EOF、退出、backpressure 与 approval association 有真实/negative fixture。

Blocked by #3774. Blocks #3776.

Canonical plan: `docs/issues/dsh-native-integration/`.

Read the canonical plan in docs/issues/dsh-native-integration/ and first check the dependency on #3774. Use the listed delivery and acceptance items as the completion criteria, including versioned contracts, fail-closed mappings, one-shot resolution, and real negative fixtures for ordering, EOF, exit, backpressure, and approval association.

Written by the indexing model from the issue text.