Updated the `Program.cs` file to enhance static file handling:
- Corrected the comment for `.mjs` MIME type registration.
- Added a new MIME type mapping for `.ftl` files as `text/plain`.
- Updated `UseStaticFiles` middleware to use a `StaticFileOptions`
object with the modified `ContentTypeProvider`.
These changes ensure proper serving of `.mjs` and `.ftl` files with
appropriate content type headers.
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