refactor(board): modernize item and application select modals with SelectableCard (#6642)

Modernize board item, application, and integration selection flows with shared Mantine components, batch board actions, improved accessibility, and hardened persistence.

apps/docs/static/api/open-api-schema.json

@@ -2106,7 +2106,6 @@
                     "enum": [
                       "clock",
                       "weather",
-                      "today",
                       "airQuality",
                       "countdown",
                       "timer",