bug: "Delete" option is displayed for built-in rules despite being undeletable

[suvanl]

App and system information

- FixMyLinks app version: 1.2.1
- Android version: 14 (API 34)
- Android build number: UE1A.230829.019
- Device model: Generic AVD (Medium Phone API 34)
- Device type: Emulated

Summary of expected behaviour

There should be no way to delete a built-in rule.

Summary of actual behaviour

It's possible to "delete" a built-in rule in the same way that a custom rule can be deleted, via RuleDetailsScreen.

The rule doesn't actually get deleted, but there's nothing to indicate that a built-in rule cannot be deleted, so users may expect the rule to have been deleted successfully.

Description of what you think should be changed

The overflow menu containing the "Delete" option on RuleDetailsScreen should only be displayed for custom rules, not built-in rules.

Steps to reproduce the bug

1. Open the app
2. Go to the "Rules" destination using the bottom navigation bar
3. Tap the "Built-in" tab title, or swipe to it
4. Tap on any built-in rule card
5. Activate the overflow menu in the top right of the screen
6. Tap "Delete"
7. Tap "Delete" again on the confirmation dialog
8. Observe that the app navigates back to RulesScreen, just like when a custom rule is deleted.
   • Unlike custom rules, the built-in rule doesn't actually get deleted. The rule not being deleted is a good thing, because it shouldn't be possible to delete built-in rules (and at this moment in time isn't technically possible, given that BIRs are hardcoded).

Additional info

No response