Add graphical session saver

[jordanhubbard]

Goal

Preserve desktop continuity across Omarchy logins by restoring applications that can be safely launched from their desktop entries, along with their Hyprland workspace and window placement.

What this adds

• Adds omarchy-session, a user-facing command that saves, restores, watches, and reports the session state.
• Adds omarchy-session.service, tied to graphical-session.target and gated on WAYLAND_DISPLAY. It restores once when the graphical session starts, snapshots every 10 seconds while it runs, and performs a final save when it stops.
• Persists a schema-versioned JSON snapshot atomically under $XDG_STATE_HOME/omarchy/session/last.json.
• Maps Hyprland window classes to desktop entries through StartupWMClass, then restores only launchable applications using gtk-launch rather than retaining volatile process data.
• Restores workspace, floating state, floating size and position, and fullscreen state after each app opens.
• Excludes Omarchy Quickshell windows and strips ephemeral fields such as addresses and PIDs from saved state.
• Installs the unit in the package defaults and enables it during first-run user-unit setup.

Verification

• bash test/shell.d/session-test.sh
• bash test/shell.d/systemd-test.sh
• ./test/cli
• git diff --check

The focused session test stubs Hyprland client data and verifies durable, schema-versioned state; desktop-entry resolution; and omission of Quickshell and transient window addresses.