fix: prevent duplicate elements in LaunchScreen.storyboard on repeated runs

[Copilot]

Description

Running dart run splash_master create multiple times duplicated elements in LaunchScreen.storyboard, causing invalid XML that breaks iOS builds.

Changes

• Fix duplicate background image element (lib/cmd/ios_splash.dart)

  • Added check for existing background image element with id edQ-YT-iED before creating a new one
  • Prevents duplicate background image elements from accumulating on subsequent runs
  • Calls getBackgroundImageElement(subViews) to verify element doesn't exist before creation

• Fix constraint cleanup logic (lib/cmd/ios_splash.dart)

  • Changed from remove(getElement()) to removeWhere() at lines 178-183 and 216-221
  • Previous implementation only removed first constraints element; new implementation removes all instances before adding new ones

This makes the command idempotent—multiple runs produce identical, valid output without duplicate elements.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

Closes #80

Original prompt

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This section details on the original issue you should resolve

<issue_title>Executing create command always updates storyboard</issue_title>
<issue_description>Describe the bug
Running the command dart run splash_master create always updates the LaunchScreen.storyboard file by adding duplicate entries. After running the command multiple times, these duplicate nodes accumulate and cause the storyboard to become invalid.

To Reproduce
Steps to reproduce the behavior:

1. Run dart run splash_master create
2. Run the same command again
3. Open and inspect the LaunchScreen.storyboard file
4. Notice that duplicate entries have been added

Expected behavior
The command should check whether the corresponding fields or nodes already exist in the storyboard.
If an entry exists, it should be replaced or updated, It should not append a new duplicate entry. This ensures the storyboard remains valid even when the command is executed multiple times.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Executing create command always updates storyboard #80

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[ujas-m-simformsolutions]

dont remove this constraint

[Copilot]

Restored the constraint in commit d214e27.

[ujas-m-simformsolutions]

the command adds duplicate image with id edQ-YT-iED

[Copilot]

Fixed in commit d214e27. Added logic to check for existing background image element in the storyboard before creating a new one, preventing duplicates.