fix(backends): bound temporary scratch files (#11941)

Backend processes shared the host temporary directory, so crashes could leave request images and audio behind until the filesystem filled. Give each process a locked LocalAI-owned runtime, remove scratch on exit, and sweep only marked abandoned runtimes at the next start.

Also close known request error-path leaks in the Python media backends, CrispASR, LongCat Video, and stable-diffusion.cpp.

Assisted-by: Codex:gpt-5

Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

backend/python/common/temp_utils.py

@@ -0,0 +1,36 @@
+import base64
+import contextlib
+import os
+import tempfile
+
+
+@contextlib.contextmanager
+def materialize_base64(data, suffix=""):
+    """Materialize base64 data for a path-only library and always remove it."""
+    descriptor, path = tempfile.mkstemp(prefix="localai-media-", suffix=suffix)
+    try:
+        with os.fdopen(descriptor, "wb") as output:
+            descriptor = None
+            output.write(base64.b64decode(data))
+        yield path
+    finally:
+        if descriptor is not None:
+            os.close(descriptor)
+        try:
+            os.remove(path)
+        except OSError:
+            pass
+
+
+@contextlib.contextmanager
+def cleanup_paths():
+    """Collect temporary paths and remove them on success or failure."""
+    paths = []
+    try:
+        yield paths
+    finally:
+        for path in paths:
+            try:
+                os.remove(path)
+            except OSError:
+                pass