- pysimFsInfoHtml puts the FID/type/size line inside the fieldset, so the
selected file is one bordered block with its symbolic name in the border;
files without an FCI keep the plain borderless line.
- The content pane starts hidden and is synced after every mutation
(selection clears it, read success shows it, read failure keeps it hidden,
edit/cancel re-sync): no empty box before a read or edit.
- tests: FCI ordering assertions; new fs_read.test.js (visibility helper,
read success/failure/throw, markup + call sites); fs_edit extraction.
