Replaced file_picker's Load/Browse with a custom NativePickerRegistrar
Swift plugin that opens NSOpenPanel with showsHiddenFiles = true.
The file_picker package hardcodes this to false, making hidden folders
like ~/.claude invisible in its dialogs.
Changes:
- New NativePickerRegistrar.swift: custom NSOpenPanel with hidden files
- New NativePicker Dart service using method channel
- Browse: only shows folders (canChooseFiles=false), hidden visible
- Load: only shows .jsonl files, hidden folders visible
- Registered via AppDelegate.applicationDidFinishLaunching
- Removed file_picker dependency from home_screen imports
- Fixed all info-level lint issues (super params, null-aware, doc comment)
- Signed, notarized, stapled DMG
780ef9378f