Fix daemon startup when --user changes, and document service accounts

launchd opens StandardOutPath/StandardErrorPath as the service user. Re-running
install.sh with a different --user leaves those files owned by the previous
one, so the job fails to start -- and since it never gets far enough to write
anything, the log gives no clue why. Chown them before bootstrapping.

README now documents the full dedicated-service-account setup, including the
two things that are easy to get wrong: macOS home directories are drwxr-x--- so
the checkout has to live outside one, and the HuggingFace cache follows HOME so
it has to move with the service user.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

install.sh

@@ -162,6 +162,14 @@ cat > "$TMP_PLIST" <<EOF
 EOF
 
 plutil -lint "$TMP_PLIST" >/dev/null || die "generated plist is malformed"
+
+# launchd opens the log paths as the service user. If they already exist owned
+# by someone else -- which is exactly what happens when you re-run with a
+# different --user -- the job fails to start, and because it never gets far
+# enough to write anything, the log gives no clue why.
+for log in "/tmp/$LABEL.stdout" "/tmp/$LABEL.stderr"; do
+    [[ -e "$log" ]] && sudo chown "$SERVICE_USER" "$log"
+done
 sudo cp "$TMP_PLIST" "$PLIST"
 sudo chown root:wheel "$PLIST"
 sudo chmod 644 "$PLIST"