remove the desktop-pet system

The pet feature was three loosely coupled subsystems that no core flow
depended on: the Petdex catalog page, the pet install/preference store, and
the pet-state socket. All three are removed.

The only cross-boundary touch point was a try/catch-wrapped observer that
mapped chat-run events to pet animations. Removing it leaves the /chat-run
event contract unchanged: no event name, field name, field type, or emission
timing changed.

Removing petdexPublicRoutes also closes the unauthenticated outbound proxy
at /api/hermes/petdex/asset, which shrinks the SSRF surface.

docs/known-issues.md

@@ -199,7 +199,7 @@
 
 ### 视觉细节
 
-- **圆角 tag**：naive 的 `NTag round` 无 Arco 对应，改用了 `border-radius: 999px`（`PetdexView.vue`、`DevicesView.vue`）
+- **圆角 tag**：naive 的 `NTag round` 无 Arco 对应，改用了 `border-radius: 999px`（`DevicesView.vue`）
 - **按钮尺寸**：naive 的 `size="tiny"` → Arco `size="mini"`，可能与相邻元素不齐
 - **滚动条**：naive 的 `:native-scrollbar="false"` 无对应，已删除，滚动条样式会变