fix(permissions): admin can no longer operate tests — start/submit/edit/create, view only

Admin still bypassed require_any_role (non-strict) on the pure
operator actions: start-execution, submit-red, start-blue-work,
submit-blue, pause/resume-timer, and the red/blue field-edit + general
test create/update/remediation/import-rt/template endpoints all used
the loose dependency even where admin wasn't in the role tuple.
Switched every one of these to require_any_role_strict, matching the
review/validate/dispute/hold/assign endpoints already fixed earlier.

Frontend: removed every remaining role === "admin" disjunct gating
Start Execution, Submit to Blue Team, blue evaluating actions, timer
control, red/blue field editing, test creation, and template creation.
Team-blindness visibility (isBlind) deliberately keeps the admin
bypass — admin still sees both sides unmasked for oversight, since
that's visibility, not operating.

Updated ~20 tests whose fixtures used the admin account as a
convenience shortcut to create/drive tests through the workflow —
switched them to a red_lead account, fixing an incidental
fixture-resolution-order cookie bug along the way (client's cookie
jar prefers the last-logged-in role's cookie over any Bearer header
explicitly passed to a later request).

frontend/src/pages/TestsPage.tsx

@@ -139,8 +139,8 @@ export default function TestsPage() {
   const navigate = useNavigate();
   const { user } = useAuth();
 
-  const canCreate =
-    user?.role === "admin" || user?.role === "red_lead" || user?.role === "blue_lead";
+  // Only leads can create tests — admin administers the site, not test content.
+  const canCreate = user?.role === "red_lead" || user?.role === "blue_lead";
 
   const techRole = isTechRole(user?.role);