[local_auth] Convert example app to Swift

[stuartmorgan-g]

Replaces the Obj-C example app with Swift. Rather than attempt to modify the example in place, I started clean from the Swift template:

• deleted the ios/ directory.
• ran flutter create --platforms=ios . using current stable (3.41.0).

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[stuartmorgan-g]

Changelog/version override: Native example app template details are not relevant to clients.

[gemini-code-assist]

Code Review

This pull request converts the iOS example app for local_auth_darwin from Objective-C to Swift by regenerating the project from the latest Flutter stable template, updating project files and configurations. However, a critical vulnerability was introduced: the NSFaceIDUsageDescription key is missing from the Info.plist file. This absence will cause the app to crash when attempting biometric authentication with Face ID, making the example app non-functional on supported iOS hardware. Restoring this key is essential for the app to function correctly.