Add SPDX license identifier to all the .swift files.

[janiceferns02]

Contributor checklist

• This pull request is on a separate branch and not the main branch
• I have tested my code with the xcodebuild and swiftlint --strict commands as directed in the testing section of the contributing guide

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Description

Replaced the existing license notice with the line: // SPDX-License-Identifier: AGPL-3.0-or-later to standardise license declarations across source files.

Related issue

• Adding a licence identifier to swift files #528

[github-actions]

Thank you for the pull request!

The Scribe team will do our best to address your contribution as soon as we can. The following is a checklist for maintainers to make sure this process goes as well as possible. Feel free to address the points below yourself in further commits if you realize that actions are needed :)

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Maintainer checklist

• The linting and formatting workflows within the PR checks do not indicate new errors in the files changed

• The CI unit test workflows within the PR checks do not indicate new errors in the files changed

• The CHANGELOG has been updated with a description of the changes for the upcoming release and the corresponding issue (if necessary)

[github-actions]

First PR Commit Check

• The commit messages for the remote branch should be checked to make sure the contributor's email is set up correctly so that they receive credit for their contribution
• The contributor's name and icon in remote commits should be the same as what appears in the PR
• If there's a mismatch, the contributor needs to make sure that the email they use for GitHub matches what they have for git config user.email in their local Scribe-iOS repo (can be set with git config --global user.email "GITHUB_EMAIL")

[andrewtavis]

Switched it to GPL as my directions on which license should be included in the issue were incorrect :) Thanks for helping us out with this in two projects, @janiceferns02! Really appreciate it 😊