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

userland/lazybox/lazybox.c

@@ -41,6 +41,7 @@
 #include <kernel/ktime.h>
 #include <kernel/sub_lang.h>
 #include <kernel/cpp_kernel.h>
+#include <kernel/cpp_analytics.h>
 #include <userland/snake.h>
 #include <ipc/shm_posix.h>
 #include <net/dns_cache.h>
@@ -1328,6 +1329,15 @@ static int applet_cppbench(int argc, char** argv) {
     return cpp_run_benchmarks();
 }
 
+static int applet_cppstat(int argc, char** argv) {
+    int n = (argc >= 2) ? atoi(argv[1]) : 1;
+    if (n < 1) n = 1;
+    if (n > 32) n = 32;
+    for (int i = 0; i < n; i++) cpp_analytics_sample();
+    cpp_analytics_dump();
+    return 0;
+}
+
 static int applet_shm(int argc, char** argv) {
     (void)argc; (void)argv;
     posix_shm_dump();
@@ -2629,6 +2639,7 @@ static const lazybox_applet_t applets[] = {
     {"cpptest",       applet_cpptest,       "cpptest",                   "C++ polymorphism & new/del", "System"},
     {"cppdevs",       applet_cppdevs,       "cppdevs",                   "C++ OOP device tree",        "System"},
     {"cppbench",      applet_cppbench,      "cppbench",                  "C++ OOP benchmark suite",    "System"},
+    {"cppstat",       applet_cppstat,       "cppstat [samples]",         "C++ analytics engine stats", "System"},
     {"shm",           applet_shm,           "shm",                       "POSIX /dev/shm shared memory", "System"},
     {"dnscache",      applet_dnscache,      "dnscache [-f]",             "DNS resolver cache & metrics", "Network"},
     {"beep",          applet_beep,          "beep [freq/jingle] [ms]",   "PC speaker & HDA tone synth", "Sound"},