0.0.20

Changed

• The artisan floor names this batch's release. fluttersdk_artisan moves ^0.0.19 to ^0.0.20. The old range already admitted 0.0.20, so a fresh pub get resolves nothing differently; what changes is that the floor names the release this package is verified against. artisan 0.0.20 is not breaking, and a consumer inherits one behaviour from it: a dusk:* command run while the app is still booting, before ext.dusk.* is registered, now prints one retry line and exits 75 instead of an RPC stack and exit 3. The requirements tables in doc/getting-started/installation.md and doc/getting-started/index.md and the stack lines in CLAUDE.md and .github/copilot-instructions.md quote the new floor. (pubspec.yaml, doc/getting-started/, CLAUDE.md, .github/copilot-instructions.md)