rsnix v0.5.0: graphics layer + cursor compositor

The first visible GUI surface: real rect primitives, a single
shadow→display push path, and an on-screen mouse cursor that can
never race the text surface.

gop:
- fill_rect + push_rect(x,y,w,h): every raster op rasterises into the
  RAM shadow, then push_rect copies the rect to the display (write-only,
  still never read) and composites the cursor on top. blit_glyph and
  scroll shifts now route through it.
- cursor overlay: 12x16 pointer (const-fn built from column lists) drawn
  white with a black offset outline; position in one AtomicU64 (x:high
  32, y:low 32) — unpack masks the low word (a bare 'as usize' cast is
  a no-op on 64-bit). The cursor never enters the shadow, so erasing is
  just a shadow push of the old rect.
- cursor_redraw after scroll shifts and once at spawn (the vt diff never
  re-blits idle cells).

cursor task (task 2, spawned at boot when a mouse is present):
- owns the PS/2 ring; polls every 10 ms, moves the cursor (clamped),
  tracks buttons, and forwards every event to a task's queue when
  'mouse <id>' armed it (the window-manager input path).
- /dev/mouse is now a position device (x/y/buttons snapshot); 'mouse'
  watches the cursor live (prints on change); 'cursor' prints one-shot
  state; 'gfx' draws a status-bar demo; 'gfx check' is an in-kernel
  pixel self-test (shadow readback, display readback, cursor overlay
  purity) — PASS/FAIL per stage.

Tests (headless QEMU + monitor injection):
- make test-gfx (new): all four compositor checks PASS.
- make test-mouse (rewritten): cursor tracks mouse_move deltas, buttons
  ride along, /dev/mouse snapshot, live watch, real-event queue routing.
- make test-msg: task numbering shifted (cursor is task 2; msgrecv is
  task 3) — updated, still PASS.
- make test-disk regression re-passes. 0 build warnings.

1 files changed, 4 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index f244251..9604893 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ export BOOT_EFI=$(ESP_DIR)/EFI/BOOT/BOOTX64.EFI
 # Create one with: make disk   (or: ./scripts/mkdisk.sh)
 export DISK_IMG ?= /tmp/disk.img
 
-.PHONY: all run run-gui clean image debug release fmt bootloader boot-image disk disk-fresh inspect test-disk test-mouse test-msg
+.PHONY: all run run-gui clean image debug release fmt bootloader boot-image disk disk-fresh inspect test-disk test-mouse test-gfx test-msg
 
 # ---- Build ---------------------------------------------------------------
 
@@ -118,6 +118,9 @@ test-disk:
 test-mouse:
         ./scripts/test-mouse.sh
 
+test-gfx:
+        ./scripts/test-gfx.sh
+
 # Automated scheduler message-queue round trip: msgrecv/send, real-input
 # routing into a task's queue, queue-full boundary.
 test-msg: