feat(rust,gui): RLE compression codec + Rust Lab desktop app

Rust kernel expansion:
- rust/src/compress/mod.rs (new): memory-safe PackBits-style run-length
  encoding codec (rle_compress / rle_decompress) with C-ABI shims, registered
  in lib.rs. C fallbacks added to rust_fallback.c so aarch64/armv8i match.
- include/kernel/rust.h: FFI declarations for the codec.
- LazyBox: new `rle <text>` applet that compresses, decompresses, prints the
  ratio and verifies the round-trip is lossless.

GUI expansion:
- gui/gui_apps.c: "Rust Lab" app -- a live dashboard for the Rust subsystem.
  Shows CRC-32C/Adler-32 of a sample, measured ChaCha20/SHA3-256/AES-128
  throughput as scaled bars plus a composite score (benchmark run once at
  launch and cached), and a live ChaCha20 CSPRNG byte stream refreshed
  periodically. Per-window state freed on close.
- Registered "Rust Lab" (info icon) in the desktop app table and on the
  desktop; desktop icon indices updated for the new entry.

Verified: clean build on x86_64/aarch64/armv8i; boots through the SUB login to
the desktop with the new Rust Lab icon rendering (screenshotted); checksum
self-test prints, 0 panics / 0 OOM.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Fh5z6V7nGPbHvqVG5p4CXX

gui/gui_desktop.c

@@ -57,6 +57,7 @@ static const desktop_app_t g_apps[] = {
     { "Calculator", GUI_ICON_CALC,     gui_app_calc_launch,     260, 100, 220, 240 },
     { "Paint",      GUI_ICON_PAINT,    gui_app_paint_launch,    200,  60, 360, 260 },
     { "Life",       GUI_ICON_FLASK,    gui_app_life_launch,     240,  70, 480, 380 },
+    { "Rust Lab",   GUI_ICON_INFO,     gui_app_rustlab_launch,  300,  80, 420, 300 },
     { "Clock",      GUI_ICON_CLOCK,    gui_app_clock_launch,    460, 120, 280, 260 },
     { "Settings",   GUI_ICON_SETTINGS, gui_app_settings_launch, 160,  60, 400, 320 },
     { "About",      GUI_ICON_INFO,     gui_app_about_launch,    240, 140, 330, 170 },
@@ -64,8 +65,9 @@ static const desktop_app_t g_apps[] = {
 #define APP_COUNT ((int)(sizeof(g_apps) / sizeof(g_apps[0])))
 
 // Which of the above appear on the desktop itself.
-// Indices into g_apps[]: Terminal, Files, Monitor, Kernel Log, KTest, Life, Settings.
-static const int g_desktop_icons[] = { 0, 1, 2, 4, 5, 9, 11 };
+// Indices into g_apps[]: Terminal, Files, Monitor, Kernel Log, KTest, Life,
+// Rust Lab, Settings.
+static const int g_desktop_icons[] = { 0, 1, 2, 4, 5, 9, 10, 12 };
 #define DESKTOP_ICON_COUNT ((int)(sizeof(g_desktop_icons) / sizeof(g_desktop_icons[0])))
 
 static bool g_start_menu_open   = false;