feat(sidecars): add proxied sidecar tabs (#279)

## Summary
- add SideCar support across the server and UI, including proxied tabs,
picker/settings flows, and websocket-aware proxying
- unify top-level tab handling so workspace instances and SideCars share
the same tab model and navigation flows
- limit SideCars to port-based services only, removing server-managed
process control from the final API and UI

---------

Co-authored-by: Shantur <shantur@Mac.home>
Co-authored-by: Shantur <shantur@Shanturs-MacBook-Pro-M5.local>

packages/ui/src/components/message-block.tsx

@@ -9,7 +9,7 @@ import type { MessageRecord } from "../stores/message-v2/types"
 import { messageStoreBus } from "../stores/message-v2/bus"
 import { formatTokenTotal } from "../lib/formatters"
 import { sessions, setActiveParentSession, setActiveSession } from "../stores/sessions"
-import { setActiveInstanceId } from "../stores/instances"
+import { selectInstanceTab } from "../stores/app-tabs"
 import { showAlertDialog } from "../stores/alerts"
 import { deleteMessage } from "../stores/session-actions"
 import { useI18n } from "../lib/i18n"
@@ -130,7 +130,7 @@ function findTaskSessionLocation(sessionId: string, preferredInstanceId?: string
 }
 
 function navigateToTaskSession(location: TaskSessionLocation) {
-  setActiveInstanceId(location.instanceId)
+  selectInstanceTab(location.instanceId)
   const parentToActivate = location.parentId ?? location.sessionId
   setActiveParentSession(location.instanceId, parentToActivate)
   if (location.parentId) {