fix(gui): Adapt the desktop to the active resolution and restore the console on exit

The launcher table is authored against an 800x600 work area, so at 1280x720
every window kept its original size and left the desktop looking sparse, while
still overlapping the icon column the way it did at the design resolution.
Launch geometry now scales with the work area, capped so a window cannot
swallow the screen, and offset clear of the icon strip so launcher labels stay
readable.

The wallpaper grid was a single fixed colour, which is darker than the top of
the gradient but lighter than the bottom, so the grid faded out across the
lower half of the screen. It is blended now and reads the whole way down.

Leaving the desktop hands the screen to the framebuffer console, and entering
it takes the screen back, so Esc drops to a working TTY inside the emulator and
`gui` returns to the desktop.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP

README.md

@@ -47,6 +47,11 @@
   - **Animated progress bar** tied to the real boot stages, held for a minimum duration (`splashtime=<ms>`) so a sub-second boot still shows it; `nosplash`, `nogui` or `text` skip it.
   - **Regenerable**: `python3 scripts/mklogo.py path/to/logo.png` rewrites `init/logo_data.c` from source artwork.
 - 🔤 **Shared 8x8 Console Font (`lib/font8x8.c`)**: one glyph table behind the framebuffer console, the 2D canvas rasterizer and the desktop compositor, replacing three divergent private copies.
+- 🖵 **Framebuffer Console (`drivers/video/fbcon.c`)**:
+  - Once the VBE adapter is in graphics mode the VGA text buffer stops being scanned out, so anything printed afterwards is invisible on the display even though it still reaches serial. fbcon renders the console into the framebuffer instead, the way Linux fbcon does.
+  - **VT100 subset**: SGR colours, cursor addressing (`H`/`f`), relative moves, erase-display and erase-line, save/restore — enough for full-screen curses-style programs such as the **nano** editor to render correctly.
+  - Presents a fixed **80x25** grid (matching `TTY_WIDTH`/`TTY_HEIGHT`, which the userland assumes) with the glyph cell scaled to fill whatever resolution is active.
+  - The TTY driver dispatches `tty_write`, `tty_clear` and `tty_set_cursor` to it, so leaving the desktop with `Esc` drops to a working console **inside the emulator**, not just on the host serial line.
 - 🖥️ **SUB-OS Graphical Desktop Environment (`gui/`)**:
   - **SUB-WM Compositor**: 800x600 TrueColor double-buffered window manager with drag, corner resize, minimize/maximize/restore, edge snapping (left/right/maximize), tile and cascade layouts, and z-ordered painter's-algorithm compositing.
   - **SUB-WT Widget Toolkit (`gui/gui_widgets.c`)**: Immediate-mode controls -- buttons, labels, checkboxes, radios, sliders, list boxes, text fields, tab bars, scrollbars, progress bars, sparklines and badges -- so an app rebuilds its interface from state each frame instead of maintaining a retained widget tree.
@@ -231,9 +236,14 @@ SUB-OS boots straight into the desktop. Pass `nogui`, `text`, `emergency` or
 from inside the desktop, `Esc` (or Start -> Exit to Kernel TTY) drops to the
 same shell.
 
+The display mode is set with `video=WIDTHxHEIGHT` on the kernel command line
+(default `1280x720`, 16:9). Both the desktop and the framebuffer console adapt
+to whatever mode is active.
+
 ```bash
-make run-gui     # Local SDL/GTK window
-make run-vnc     # Headless: VNC server on localhost:5900
+make run-gui         # Windowed, aspect-preserving scaling
+make run-fullscreen  # Fullscreen without stretching
+make run-vnc         # Headless: VNC server on localhost:5900
 ```
 
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