feat(mesh): refine the Routing tab and add per-route removal (#1311)

* feat(mesh): refine the Routing tab and add per-route removal

Tighten the Fleet > Routing tab so its node cards and diagnostics read
honestly for proxy-connected fleets, and remove a couple of dead ends.

- Node cards drop the "pilot connected/offline" line, which was meaningless
  for nodes that connect over the HTTP API proxy. The compact card drops the
  matching agent cell and now reads stacks / aliases / bridge.
- Enabling mesh on a proxy node shows a transient "Connecting" state and
  settles to meshed on its own, instead of flashing "Degraded" with a manual
  refresh while the bridge finishes dialing.
- The alias detail sheet gains a "Remove from mesh" action that opts the
  alias's owning stack out (the confirmation says how many aliases that
  drops), and a "Topology" tab. The standalone topology sheet and its
  opt-in-sheet shortcut are removed in favor of the tab.
- The "Add stack" affordance stays reachable on a meshed node, so a node
  that already has aliases is no longer a dead end.
- Diagnostics and the alias detail sheet show a transport-aware line
  ("local", "API proxy bridge", or "Pilot tunnel" with its state) instead of
  a fixed "Pilot tunnel" label.

Adds unit coverage for the new state derivation, transport descriptor, the
enable auto-converge, and the admin-gated removal, and updates the mesh docs.

* fix(mesh): harden Routing tab toggle and alias sheet against async races

Independent review surfaced two narrow async races in the new code.

- RoutingNodeCard: cancel the converge re-poll batch at the start of any
  toggle (so a slow disable can't let a prior enable's re-polls fire), and
  guard the toast, refresh, timer scheduling, and setToggling behind a mounted
  ref so nothing runs after the card unmounts while the enable POST is still
  in flight.
- MeshRouteDetailSheet: re-check the cancelled flag after reading the
  diagnostic body, not just before it. Reading the body is itself async, so a
  superseded alias's diagnostic could otherwise call setDiag and expose Remove
  for the wrong stack.

Adds tests for unmount-before-enable-resolves and the deferred-diagnostic
alias switch.

frontend/src/components/fleet/MeshOptInSheet.tsx

@@ -5,7 +5,7 @@ import { SystemSheet } from '@/components/ui/system-sheet';
 import { Button } from '@/components/ui/button';
 import { ConfirmModal } from '@/components/ui/modal';
 import type { MeshStackEntry } from '@/types/mesh';
-import { Loader2, Workflow } from 'lucide-react';
+import { Loader2 } from 'lucide-react';
 
 interface Props {
     open: boolean;
@@ -13,12 +13,11 @@ interface Props {
     nodeId: number;
     nodeName: string;
     onChanged: () => void;
-    onViewTopology?: (stack: string) => void;
     /** Opt-in/out is admin-only on the backend; non-admins see the list read-only. */
     canManage: boolean;
 }
 
-export function MeshOptInSheet({ open, onOpenChange, nodeId, nodeName, onChanged, onViewTopology, canManage }: Props) {
+export function MeshOptInSheet({ open, onOpenChange, nodeId, nodeName, onChanged, canManage }: Props) {
     const [stacks, setStacks] = useState<MeshStackEntry[]>([]);
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState<string | null>(null);
@@ -125,16 +124,6 @@ export function MeshOptInSheet({ open, onOpenChange, nodeId, nodeName, onChanged
                                     <Loader2 className="w-4 h-4 animate-spin text-stat-subtitle" />
                                 ) : (
                                     <div className="flex items-center gap-2">
-                                        {stack.optedIn && onViewTopology && (
-                                            <Button
-                                                size="sm"
-                                                variant="ghost"
-                                                onClick={() => onViewTopology(stack.name)}
-                                                aria-label={`View topology for ${stack.name}`}
-                                            >
-                                                <Workflow className="w-3 h-3 mr-1" /> Topology
-                                            </Button>
-                                        )}
                                         {canManage && (
                                             <Button
                                                 size="sm"