feat: session management fixes and sessions hub

- Add confirmation dialogs for stop/delete on dashboard
- Filter deleted sessions immediately without reload
- Add tunnel health polling with error badges
- Add Sessions nav item with active count badge
- Route /sessions to SessionsPage component

Quality gates: 43/43 tests pass, typecheck pass, lint pass

Refs: openspec/changes/session-management-fixes
Refs: openspec/changes/sessions-hub

apps/web/src/components/app-shell.tsx

@@ -9,8 +9,9 @@ import { useSessions } from "../state/sessions";
 import { Icon } from "./icon";
 import type { IconName } from "../utils/icons";
 
-const NAV_ITEMS: { to: string; label: string; icon: IconName }[] = [
+const NAV_ITEMS: { to: string; label: string; icon: IconName; badge?: "sessions" }[] = [
   { to: "/", label: "Home", icon: "dashboard" },
+  { to: "/sessions", label: "Sessions", icon: "terminal", badge: "sessions" },
   { to: "/projects", label: "Projects", icon: "projects" },
   { to: "/tool-workshop", label: "Tool Workshop", icon: "settings" },
   { to: "/settings", label: "Settings", icon: "settings" }
@@ -83,7 +84,6 @@ export const AppShell = () => {
       <div className="shell-body">
         <aside className="shell-nav" aria-label="Primary navigation">
           {NAV_ITEMS.map((item) => {
-            const isHome = item.to === "/";
             const activeCount = sessions.filter((s) => s.status === "running").length;
             return (
               <NavLink
@@ -94,7 +94,7 @@ export const AppShell = () => {
               >
                 <Icon name={item.icon} size="sm" />
                 {item.label}
-                {isHome && activeCount > 0 && (
+                {item.badge === "sessions" && activeCount > 0 && (
                   <span className="nav-badge">{activeCount}</span>
                 )}
               </NavLink>