feat(FN-2585): remove top-level remote access toggle

- Remove the standalone remoteEnabled setting from CLI, core settings defaults/types, and dashboard settings APIs/UI
- Treat remote access as enabled when an active provider is selected and that provider is configured as enabled
- Update remote auth and engine lifecycle checks to gate on provider activation instead of a global flag
- Adjust tests and add a changeset documenting the remote access configuration simplification

packages/core/src/settings-schema.ts

@@ -157,7 +157,6 @@ export const DEFAULT_PROJECT_SETTINGS = {
   agentPrompts: undefined,
   promptOverrides: undefined,
   remoteAccess: {
-    enabled: false,
     activeProvider: null,
     providers: {
       tailscale: {