Clients that connect but never send messages or subscribe to events
would accumulate indefinitely, eventually exhausting file descriptors.

Add tracking for client creation time and last activity timestamp.
Clients are now cleaned up if they have been idle for 60+ seconds
without subscribing to any events or sending any messages.

This approach is safer than treating UnexpectedEof as disconnect,
which caused issues with polybar's connection handling.

- Add gradient border, animation, and shader config options
- Add frame gradient rendering code (currently disabled)
- Fix frame destruction to unmap before destroy
- Gradient borders disabled due to lifecycle issues

Enable proper systemd user service integration:
- Import DISPLAY and XAUTHORITY to systemd user session
- Update D-Bus activation environment
- Start gar-session.target (binds to graphical-session.target)

This allows user services like garbg.service to start reliably
at login with access to the X11 display. The gar-session.target
is needed because graphical-session.target has RefuseManualStart=yes.

Pattern follows sway-systemd, i3-session, and ArchWiki systemd/User.

- Add --backend glx to picom commands (required for v12+, no default)
- Add cursor_move (fleur) for floating window drag operations
- Add clear_window_cursor() to prevent grab/window cursor conflicts
- Pass appropriate cursor to grab_pointer() during drag/resize
- Restore edge cursor after drag release
- Add cursor_for_edge() helper for resize cursor selection

- Support both Alt and Super mod keys for drag operations
- Add resize cursors for all edges and corners
- Change cursor on hover near floating window edges
- Click and drag edges to resize without mod key
- Keep button grabs on floating windows for edge detection

Only report workspaces that are visible or have windows to polybar,
matching i3 behavior. Empty invisible workspaces are now filtered out.

- Add WorkspaceNext/WorkspacePrev to Action enum
- Cycle only through workspaces with windows (skip empty ones)
- Add gar.workspace_next() and gar.workspace_prev() Lua bindings

Only process UnmapNotify when event.event == root (SubstructureNotify).
Ignore events sent directly to window (StructureNotify) to prevent
double-processing which caused windows to be unmanaged incorrectly.

Track intentional unmaps with ignore_unmap_count to prevent
UnmapNotify handler from unmanaging windows we're just hiding.

- Set target workspace focus before switch_workspace in move_to_workspace
- Add set_focus after swap and cross-monitor fallback in swap_direction
- Call set_focus after move_to_monitor to update X11 focus

Warp pointer in-place after setting root cursor to ensure X11
redraws the cursor with our definition, clearing any stale cursor
images from the display manager.

- Move button grab/ungrab into set_focus() to ensure clicks reach apps
- Don't warp pointer on _NET_ACTIVE_WINDOW (user is already interacting)

Useful when dock/panel struts are incorrect (e.g., notch offset on Asahi).
Set gar.set("bar_height", N) in config to reserve N pixels at top.