Fix React CSS property conflict in availability page

- Replaced borderColor with full border property in dayCardActive
- Replaced borderColor with full border property in dayCardSource
- Replaced borderColor with full border property in dayCardTarget
- Prevents React warning about mixing shorthand and non-shorthand properties
- Fixes console error when using 'Clear all' button on availability page

.cursor/rules/running_tests.mdc

@@ -6,3 +6,8 @@ alwaysApply: false
 There are backend, frontend and e2e tests.
 
 They should be run with the `test-` commands found in the `Makefile`.
+
+Use the `TEST` variable to select specific tests:
+- Backend: `make test-backend TEST="tests/test_booking.py"` or `TEST="tests/test_booking.py::TestClass::test_method"`
+- Frontend: `make test-frontend TEST="app/login"` (file pattern)
+- E2E: `make test-e2e TEST="auth"` (matches e2e/auth.spec.ts)

frontend/app/admin/availability/page.tsx

@@ -446,15 +446,15 @@ const pageStyles: Record<string, React.CSSProperties> = {
   },
   dayCardActive: {
     background: "rgba(99, 102, 241, 0.1)",
-    borderColor: "rgba(99, 102, 241, 0.3)",
+    border: "1px solid rgba(99, 102, 241, 0.3)",
   },
   dayCardSource: {
     background: "rgba(34, 197, 94, 0.15)",
-    borderColor: "rgba(34, 197, 94, 0.5)",
+    border: "1px solid rgba(34, 197, 94, 0.5)",
   },
   dayCardTarget: {
     background: "rgba(99, 102, 241, 0.2)",
-    borderColor: "rgba(99, 102, 241, 0.6)",
+    border: "1px solid rgba(99, 102, 241, 0.6)",
   },
   dayCardWeekend: {
     opacity: 0.7,