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/i18n/messages/en/commands.ts

@@ -15,17 +15,17 @@ export const commandMessages = {
   "commands.newInstance.description": "Open folder picker to create new instance",
   "commands.newInstance.keywords": "folder, project, workspace",
 
-  "commands.closeInstance.label": "Close Instance",
-  "commands.closeInstance.description": "Stop current instance's server",
-  "commands.closeInstance.keywords": "stop, quit, close",
+  "commands.closeInstance.label": "Close Tab",
+  "commands.closeInstance.description": "Close the current top-level tab",
+  "commands.closeInstance.keywords": "stop, quit, close, tab",
 
-  "commands.nextInstance.label": "Next Instance",
-  "commands.nextInstance.description": "Cycle to next instance tab",
-  "commands.nextInstance.keywords": "switch, navigate",
+  "commands.nextInstance.label": "Next Tab",
+  "commands.nextInstance.description": "Cycle to the next top-level tab",
+  "commands.nextInstance.keywords": "switch, navigate, tab",
 
-  "commands.previousInstance.label": "Previous Instance",
-  "commands.previousInstance.description": "Cycle to previous instance tab",
-  "commands.previousInstance.keywords": "switch, navigate",
+  "commands.previousInstance.label": "Previous Tab",
+  "commands.previousInstance.description": "Cycle to the previous top-level tab",
+  "commands.previousInstance.keywords": "switch, navigate, tab",
 
   "commands.newSession.label": "New Session",
   "commands.newSession.description": "Create a new parent session",

packages/ui/src/lib/i18n/messages/en/folderSelection.ts

@@ -69,4 +69,5 @@ export const folderSelectionMessages = {
   "folderSelection.servers.dialog.connecting": "Connecting...",
   "folderSelection.servers.dialog.errorRequired": "Server name and URL are required.",
   "folderSelection.servers.dialog.errorConnect": "Could not connect to the remote server.",
+  "folderSelection.sidecars.button": "Open SideCar",
 } as const

packages/ui/src/lib/i18n/messages/en/settings.ts

@@ -195,4 +195,40 @@ export const settingsMessages = {
   "settings.speech.save.saved": "Saved",
   "settings.speech.save.unsaved": "Unsaved changes",
   "settings.speech.save.error": "Save failed",
+  "settings.nav.sidecars": "SideCars",
+  "settings.section.sidecars.eyebrow": "Server services",
+  "settings.section.sidecars.title": "SideCars",
+  "settings.section.sidecars.subtitle": "Configure local services listening on fixed ports that the server can proxy into tabs.",
+  "sidecars.form.name": "Name",
+  "sidecars.form.validation": "Enter a valid SideCar name and port.",
+  "sidecars.form.port": "Port",
+  "sidecars.form.insecure": "Use HTTP",
+  "sidecars.form.protocol": "Protocol",
+  "sidecars.form.protocol.help": "Choose how the proxy should connect to the local service.",
+  "sidecars.form.protocol.https": "HTTPS",
+  "sidecars.form.protocol.http": "HTTP",
+  "sidecars.form.prefixMode": "Prefix mode",
+  "sidecars.form.prefixMode.help": "Choose whether the SideCar receives the public /sidecars path prefix.",
+  "sidecars.form.prefixMode.strip": "Strip prefix",
+  "sidecars.form.prefixMode.preserve": "Preserve prefix",
+  "sidecars.form.add": "Add SideCar",
+  "sidecars.kind.port": "Port",
+  "sidecars.status.running": "Running",
+  "sidecars.status.stopped": "Stopped",
+  "sidecars.basePath": "Base path",
+  "sidecars.settings.listTitle": "Configured SideCars",
+  "sidecars.settings.listSubtitle": "Review the port-based SideCars available in the picker.",
+  "sidecars.settings.empty": "No SideCars configured yet.",
+  "sidecars.picker.title": "Open SideCar",
+  "sidecars.picker.loading": "Loading SideCars...",
+  "sidecars.picker.subtitle": "Choose an available SideCar to open in a new tab.",
+  "sidecars.picker.empty": "No port-based SideCars are available yet.",
+  "sidecars.picker.close": "Close",
+  "sidecars.open.errorTitle": "Unable to open SideCar",
+  "sidecars.open.notFound": "SideCar not found.",
+  "sidecars.open.notRunning": "SideCar is not reachable on its configured port.",
+  "sidecars.back": "Back",
+  "sidecars.refresh": "Refresh",
+  "sidecars.path": "Path",
+  "sidecars.go": "Go",
 } as const