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/styles/panels/tabs.css

@@ -154,6 +154,31 @@
   ring-offset-color: var(--surface-base);
 }
 
+.tab-pill {
+  @apply inline-flex items-center gap-1 px-3 py-2 rounded-t-md max-w-[220px] text-sm;
+  background-color: var(--tab-inactive-bg);
+  color: var(--tab-inactive-text);
+  border-bottom: 2px solid var(--tab-active-bg);
+}
+
+.tab-pill-active {
+  background-color: var(--tab-active-bg);
+  color: var(--tab-active-text);
+  border-bottom-color: var(--accent-primary);
+}
+
+.tab-pill-button {
+  @apply truncate;
+}
+
+.tab-pill-close {
+  @apply inline-flex items-center justify-center rounded w-5 h-5 text-xs;
+}
+
+.tab-pill-close:hover {
+  background-color: var(--new-tab-hover-bg);
+}
+
 /* Session tabs */
 .session-tab-base {
   @apply inline-flex items-center gap-2 px-3 py-1.5 rounded-t-md max-w-[150px] transition-colors text-sm;