feat(dashboard): GuruConnect v2 Sessions view (pass 2)

Active-sessions table with consent-state badges, viewer-token Join,
and disconnect, built on the v2 session API and existing UI primitives.

- Sessions table: machine, mode (managed/attended), consent badge
  (granted/pending+pulse/denied/not_required), viewers, started,
  duration, status. Sticky header, skeleton load, empty/error states.
- Join action mints a session-scoped viewer token
  (POST /api/sessions/:id/viewer-token) and reveals it with the
  /ws/viewer relay URL and copy buttons. The static viewer.html is
  intentionally not targeted: it sends the raw login JWT, which the v2
  viewer plane rejects. In-dashboard web viewer ships in a later pass.
- Authz split mirrors the server mint gate: admin or control permission
  gets Control; view permission gets View only; neither hides the action.
  Server remains authoritative; the minted token carries the signed
  access claim.
- Disconnect via confirm dialog (DELETE /api/sessions/:id), invalidates
  the sessions query. List polls every 8s so consent transitions surface.

Passed Code Review (no blockers) and local gates (tsc/lint/build green).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

dashboard/src/components/layout/icons.tsx

@@ -111,3 +111,19 @@ export function CopyIcon(props: IconProps) {
     </svg>
   );
 }
+
+export function JoinIcon(props: IconProps) {
+  return (
+    <svg {...base(props)}>
+      <path d="M15 3h4a2 2 0 0 1 2 2v14a2 2 0 0 1-2 2h-4M10 17l5-5-5-5M15 12H3" />
+    </svg>
+  );
+}
+
+export function StopIcon(props: IconProps) {
+  return (
+    <svg {...base(props)}>
+      <rect x="5" y="5" width="14" height="14" rx="2" />
+    </svg>
+  );
+}