Sign panel sessions and isolate test runs

- Replace in-memory auth sessions with signed cookies and signed OAuth state
- Add auth route coverage and update panel/web server wiring
- Switch test script to per-file Bun processes and clean up type checks

shared/scripts/simulate-ci.sh

@@ -92,7 +92,7 @@ if [ -n "$1" ]; then
         EXIT_CODE=1
     fi
 else
-    if bash shared/scripts/test-sequential.sh --integration; then
+    if bash shared/scripts/test-isolated.sh --integration; then
         echo "✅ CI Simulation Passed!"
         EXIT_CODE=0
     else