container: Report tool installer failures without a traceback

A failing official installer aborted with a raw CalledProcessError
traceback, burying the actual problem the installer had already printed
to the terminal. Exit with a short message pointing at that output
instead.

agent-container.py

@@ -243,6 +243,7 @@ class AgentContainer:
                 f"Installing {tool} into the container home "
                 "(official installer, no sudo)..."
             )
+            try:
                 subprocess.run(
                     [
                         "docker", "exec", self.container_name, "bash", "-lc",
@@ -250,6 +251,12 @@ class AgentContainer:
                     ],
                     check=True,
                 )
+            except subprocess.CalledProcessError as e:
+                logger.error(
+                    f"Installing {tool} failed with exit status "
+                    f"{e.returncode}; see the installer output above."
+                )
+                sys.exit(1)
         paths = spec["path"] if isinstance(spec["path"], list) else [spec["path"]]
         for path_expr in paths:
             self._ensure_path_entry(path_expr)