Process command discovers images, builds pipeline from preset or CLI
flags (--resize, --format, --quality, --strip-metadata, --recursive),
executes with progress output, prints results with size savings, and
saves to history. Preset list/export/import use the storage module.
Processing screen with progress bar, activity log, and pause/cancel.
Results screen with stats summary, error section, and action buttons.
Settings dialog with General, Processing, Accessibility, Notifications.
Full Adwaita widget-based layouts for all 7 wizard steps with
PreferencesGroups, SwitchRows, SpinRows, ComboRows, FlowBoxes,
ExpanderRows for social media presets, quality slider with named
marks, metadata radio group, and output configuration.
7-step wizard flow (Workflow, Images, Resize, Convert, Compress,
Metadata, Output) with AdwNavigationView, step indicator dots,
Back/Next buttons, keyboard shortcuts (Alt+arrows, Alt+1-9),
and hamburger menu with Settings and History placeholders.
Preset save/load/list/delete/import/export, config JSON persistence,
session state save/restore, and processing history log with append/clear.
All stored as JSON under ~/.config/pixstrip/.
ImageLoader: load image info (dimensions, format, file size) and pixels.
Discovery: find image files by extension, flat or recursive, single file or directory.
All 9 tests passing.