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/lib/hooks/use-app-lifecycle.ts

@@ -16,6 +16,7 @@ const log = getLogger("actions")
 interface UseAppLifecycleOptions {
   setEscapeInDebounce: (value: boolean) => void
   handleNewInstanceRequest: () => void
+  handleCloseActiveTab: () => Promise<void>
   handleCloseInstance: (instanceId: string) => Promise<void>
   handleNewSession: (instanceId: string) => Promise<void>
   handleCloseSession: (instanceId: string, sessionId: string) => Promise<void>
@@ -31,7 +32,7 @@ export function useAppLifecycle(options: UseAppLifecycleOptions) {
 
     setupTabKeyboardShortcuts(
       options.handleNewInstanceRequest,
-      options.handleCloseInstance,
+      options.handleCloseActiveTab,
       options.handleNewSession,
       options.handleCloseSession,
       () => {

packages/ui/src/lib/hooks/use-commands.ts

@@ -2,7 +2,8 @@ import { createSignal, onMount } from "solid-js"
 import type { Accessor } from "solid-js"
 import type { Preferences, ExpansionPreference, ToolInputsVisibilityPreference } from "../../stores/preferences"
 import { createCommandRegistry, type Command } from "../commands"
-import { instances, activeInstanceId, setActiveInstanceId } from "../../stores/instances"
+import { activeInstanceId } from "../../stores/instances"
+import { selectNextAppTab, selectPreviousAppTab } from "../../stores/app-tabs"
 import type { ClientPart, MessageInfo } from "../../types/message"
 import { getSessions, getVisibleSessionIds, setActiveSession, setActiveSessionFromList } from "../../stores/sessions"
 import { showAlertDialog } from "../../stores/alerts"
@@ -41,6 +42,7 @@ export interface UseCommandsOptions {
   setThinkingBlocksExpansion: (mode: ExpansionPreference) => void
   setToolInputsVisibility: (mode: ToolInputsVisibilityPreference) => void
   handleNewInstanceRequest: () => void
+  handleCloseActiveTab: () => Promise<void>
   handleCloseInstance: (instanceId: string) => Promise<void>
   handleNewSession: (instanceId: string) => Promise<void>
   handleCloseSession: (instanceId: string, sessionId: string) => Promise<void>
@@ -90,9 +92,7 @@ export function useCommands(options: UseCommandsOptions) {
       keywords: () => splitKeywords("commands.closeInstance.keywords"),
       shortcut: { key: "W", meta: true },
       action: async () => {
-        const instance = activeInstance()
-        if (!instance) return
-        await options.handleCloseInstance(instance.id)
+        await options.handleCloseActiveTab()
       },
     })
 
@@ -103,13 +103,7 @@ export function useCommands(options: UseCommandsOptions) {
       category: "Instance",
       keywords: () => splitKeywords("commands.nextInstance.keywords"),
       shortcut: { key: "]", meta: true },
-      action: () => {
-        const ids = Array.from(instances().keys())
-        if (ids.length <= 1) return
-        const current = ids.indexOf(activeInstanceId() || "")
-        const next = (current + 1) % ids.length
-        if (ids[next]) setActiveInstanceId(ids[next])
-      },
+      action: () => selectNextAppTab(),
     })
 
     commandRegistry.register({
@@ -119,13 +113,7 @@ export function useCommands(options: UseCommandsOptions) {
       category: "Instance",
       keywords: () => splitKeywords("commands.previousInstance.keywords"),
       shortcut: { key: "[", meta: true },
-      action: () => {
-        const ids = Array.from(instances().keys())
-        if (ids.length <= 1) return
-        const current = ids.indexOf(activeInstanceId() || "")
-        const prev = current <= 0 ? ids.length - 1 : current - 1
-        if (ids[prev]) setActiveInstanceId(ids[prev])
-      },
+      action: () => selectPreviousAppTab(),
     })
 
     commandRegistry.register({