feat(cpp,gui): C++ Analytics Engine + live GUI Analytics app

Kernel (C++17 freestanding):
  - New Analytics Engine (kernel/cpp/cpp_analytics.cpp): templated rolling
    time-series (TimeSeries<N>) sampling four live channels -- CPU load %,
    memory %, kernel-heap %, network pkt/interval -- with windowed statistics
    (min/max/mean/stddev) computed in pure integer math (kernel is -mno-sse, so
    no FP; stddev uses a Newton integer isqrt). Demonstrates virtual dispatch
    via an Observer pattern (IAnalyticsObserver + a ThresholdAlarmObserver that
    counts breaches) and RAII singletons.
  - Extended cpp_containers.hpp with Optional<T>, Pair<A,B>, and the kmin/kmax/
    kclamp/kswap algorithms.
  - Full C fallback (cpp_fallback.c) so the engine is functionally identical on
    aarch64/armv8i, which don't build the .cpp path.
  - Wired cpp_analytics_init() into boot [8/14]; seeds a few samples so graphs
    are populated immediately.

GUI:
  - New "Analytics" desktop app (gui/gui_apps.c): a 2x2 grid of live line-charts
    backed by the C++ engine, each with gridlines, a soft baseline fill, and
    min/avg/max(/stddev) overlays; click a panel to focus one channel full-size,
    click again to return. Throttled to ~2 Hz sampling off the compositor's
    repaint cadence. Registered on the desktop and in the start menu.

Userland: new `cppstat [samples]` applet dumps the engine's per-channel stats
and Observer breach counters.

Verified in QEMU (x86_64): boots clean on x86_64/aarch64/armv8i; `cppstat`
prints live stats (CPU 6%, Mem 7%, Heap 22%, computed min/avg/max/stddev,
Observer breaches); the GUI Analytics window renders all four graphs with the
Kernel Heap curve visibly climbing 22->55% as windows open, compositor steady
at ~53 FPS.

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

kernel/main.c

@@ -83,6 +83,7 @@
 #include <kernel/rust.h>
 #include <kernel/sub_lang.h>
 #include <kernel/cpp_kernel.h>
+#include <kernel/cpp_analytics.h>
 #include <net/filter.h>
 #include <net/http.h>
 #include <net/ssh.h>
@@ -200,6 +201,7 @@ static void subos_modular_core_boot(void) {
     boot_logo_splash_progress(55, "Starting Rust, C++ and SUB-Lang engines");
     rust_kernel_init();
     cpp_kernel_init();
+    cpp_analytics_init();
     sub_kernel_init();
     prng_seed(0, 0);
     certs_init();