v0.0.1 of filegate

A Flutter plugin for native file picking and streamed file reading across Android, iOS, macOS, Windows, and Linux. Changelog excerpt: ### Added - Initial native file picker implementation for Android, iOS, and macOS. - Added Dart APIs for picking files, picking directory contents, reading file sizes, streamed file reads, progress reads, and bounded full-file reads. - Added example app pages for files, directories, and file byte previews. - Added package tests, example widget tests, macOS integration tests, and GitHub Actions CI.