fix(process): extend parent-death backstop to C++ and Python backends

The Go parent-death watcher (pkg/grpc/parentwatch.go, commit 772b435d5)
only protects backends that route through pkg/grpc. C++ and Python
backends don't, so the originally-reported case — the llama.cpp gRPC
worker surviving a non-graceful LocalAI death — was still uncovered.

Extend the same best-effort backstop to both languages, reusing the
exact mechanism and semantics:

- capture getppid() at startup, skip if already orphaned (<=1)
- a background thread polls getppid() and self-exits on reparenting
  (getppid() != orig || == 1), portable across Linux/macOS, no-op on
  Windows
- same env vars: LOCALAI_BACKEND_PARENT_WATCH (default on; falsy
  false/0/no/off disable) and LOCALAI_BACKEND_PARENT_WATCH_INTERVAL
  (default 2s; accepts Go-style durations like 500ms/2s/1m)

C++: implemented in backend/cpp/llama-cpp (the reported, most-used C++
backend) as a dependency-free header parent_watch.h, wired into
grpc-server.cpp's main() and copied at build time via prepare.sh. C++
backends have no shared server scaffolding, so other C++ backends
(ds4, ik-llama-cpp, privacy-filter, ...) are not yet covered and would
each need the same one-line include+call as follow-ups.

Python: implemented once in the shared common/parent_watch.py and armed
from common/grpc_auth.py's get_auth_interceptors() — the single helper
every one of the 35 Python backends invokes while building its gRPC
server — so all Python backends (and future ones) are covered with no
per-backend edits and no duplicated implementation.

Tests (real process-tree reparent detection, mirroring the Go test):
- backend/cpp/llama-cpp/parent_watch_test.cpp (via run-unit-tests.sh)
- backend/python/common/parent_watch_test.py (python -m unittest)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/cpp/llama-cpp/grpc-server.cpp

@@ -75,6 +75,8 @@
 #include <windows.h>
 #endif
 
+#include "parent_watch.h" // best-effort parent-death backstop (see header)
+
 
 using grpc::Server;
 using grpc::ServerBuilder;
@@ -3442,6 +3444,10 @@ int main(int argc, char** argv) {
     }
   }
 
+    // Best-effort backstop: self-terminate if the LocalAI process that spawned
+    // us dies without cleaning us up (see parent_watch.h).
+    llama_grpc::start_parent_death_watcher();
+
     server_context ctx_server;
     BackendServiceImpl service(ctx_server);