feat: add expose all windows keybinding and Alt-drag window manipulation with floating state tracking

Implement key_expose_all function bound to Alt+Space that unminimizes, unmaximizes, and unfullscreens all windows on current workspace then rearranges. Add floating_before_maximize boolean to Client struct to preserve floating state when toggling maximize. Enable Alt+LeftDrag for moving and Alt+RightDrag for resizing windows from any position with directional cursor support. Increase resize edge detection from 8 to 12 pixels. Add panel.h dependency to keys build target and update shortcut help text with new bindings.

build/keys.d

@@ -19,7 +19,7 @@ build/keys.o: src/keys.c include/keys.h include/dwn.h include/client.h \
  /usr/include/dbus-1.0/dbus/dbus-syntax.h \
  /usr/include/dbus-1.0/dbus/dbus-threads.h include/news.h \
  include/applauncher.h include/decorations.h include/demo.h \
- include/layout.h include/api.h include/marks.h
+ include/layout.h include/api.h include/marks.h include/panel.h
 include/keys.h:
 include/dwn.h:
 include/client.h:
@@ -53,3 +53,4 @@ include/demo.h:
 include/layout.h:
 include/api.h:
 include/marks.h:
+include/panel.h: