feat(rust,gui): Rust checksum engine + Game of Life desktop app

Rust kernel expansion:
- rust/src/checksum/mod.rs (new): memory-safe CRC-32C (Castagnoli), Adler-32,
  and FNV-1a-64 with thin C-ABI shims. Registered in lib.rs with a boot-time
  self-test (crc32c("SUB-OS")=0x61e96ce9, verified against a reference impl).
- include/kernel/rust.h: FFI declarations; rust/rust_fallback.c: matching C
  fallbacks so aarch64/armv8i (no native rustc target) get identical results.
- LazyBox: new `cksum <text>` applet printing all three via the Rust engine.

GUI expansion:
- gui/gui_apps.c: Conway's Game of Life -- an interactive B3/S23 cellular
  automaton with Play/Pause/Step/Random/Clear toolbar, click-to-toggle cells,
  a live generation/population readout, and a board that scales with the
  window. The Random button seeds from the Rust ChaCha20 CSPRNG. Toolbar and
  cell input are gated on the MOUSE_DOWN edge so they do not re-fire while held.
- Registered "Life" (flask icon) in the desktop app table and on the desktop.

Verified: clean build on x86_64/aarch64/armv8i; boots through the SUB login to
the desktop (screenshotted) with the checksum self-test and 0 panics/0 OOM.

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

include/gui/gui_apps.h

@@ -9,5 +9,6 @@ void gui_app_fileman_launch(int x, int y, int w, int h);
 void gui_app_calc_launch(int x, int y, int w, int h);
 void gui_app_paint_launch(int x, int y, int w, int h);
 void gui_app_about_launch(int x, int y, int w, int h);
+void gui_app_life_launch(int x, int y, int w, int h);
 
 #endif // _GUI_APPS_H

include/kernel/rust.h

@@ -71,6 +71,11 @@ typedef struct {
 int rust_kernel_init(void);
 const char* rust_kernel_status(void);
 
+// Checksums & Non-Cryptographic Hashing (Rust)
+uint32_t rust_crc32c(const uint8_t* data, size_t len);
+uint32_t rust_adler32(const uint8_t* data, size_t len);
+uint64_t rust_fnv1a64(const uint8_t* data, size_t len);
+
 // Cryptography
 int rust_chacha20_crypt(const uint8_t* key, const uint8_t* nonce, uint32_t counter, uint8_t* data, size_t len);
 int rust_csprng_get_random(uint8_t* buffer, size_t len);