feat: add user-configurable tab customization for tabs 2 and 4

[bjorkert]

Description

This PR implements user-configurable tab customization, allowing users to select what appears in tabs 2 and 4 of the tab bar. Previously, tab 2 was dynamically set based on whether remote was enabled, but now users have full control over their tab arrangement.

Changes

• Added TabSelection enum to centralize tab configuration (display name, SF symbol, storyboard identifier)
• Added storage values for tab2Selection and tab4Selection with defaults (Alarms and Nightscout respectively)
• Created TabCustomizationSettingsView for users to configure their tab preferences
• Added migration step 2 to preserve existing user preferences (Remote users get Remote in tab 2, others get Alarms)
• Updated MainViewController to use the new dynamic tab system
• Fixed Nightscout tab enable/disable logic to work regardless of tab position
• Added missing storyboard identifier for NightscoutViewController

User Experience

Users can now go to Settings → App Settings → Tab Customization to choose what appears in tabs 2 and 4 from:

• Alarms
• Remote
• Nightscout

The fixed tabs remain:

• Tab 1: Home (fixed)
• Tab 3: Snoozer (fixed)
• Tab 5: Settings (fixed)

Migration

Existing users will have their preferences preserved:

• If Remote was enabled: Tab 2 = Remote
• If Remote was disabled: Tab 2 = Alarms
• Tab 4 defaults to Nightscout for all users

Testing

• Verified tab customization works correctly
• Tested migration preserves existing user preferences
• Confirmed Nightscout tab is properly disabled when URL is empty
• Verified all tab combinations work as expected

Closes #333

[bjorkert]

ScreenRecording_07-08-2025.21-17-14_1.MP4

[codebymini]

👍 Looks and work great

[flyingpie101]

This is looking great. I still do use all 6 function though.
I wonder if we can sneak a Nightscout link somewhere , maybe as a tap on the current BG value ?

[marionbarker]

General comment about the design.

If tab selection is such that either Remote or Nightscout is not selected for one of the tabs, there is no way to get to that screen.

The alarms can be reached using the alarm row under settings.

[bjorkert]

I am working on another suggestion, hold on..

[bjorkert]

Closing this one in favor for #437