test scripts: known-file picker for the file actions

The UPDATE file / READ file step editor's path field gains the selector
the APDU builder's SELECT rows use: the loaded file-manager tree, the
custom files and the standard uicc_files.json list, merged by
rfmFileEntries, grouped by root with a filter.  Picking a file fills
test-f-path; the text field stays authoritative (a name path or an
unlisted file can still be typed) and the current path is preselected
when known.  Only EFs are offered - the action reads/writes a file, so a
DF/ADF is not a target.

v3.38.0: server.py VERSION, pyproject.toml and the PWA header;
sw cache simple-v478 (help/index changed); a CHANGELOG [3.38.0] section,
the help EN/RU, docs/test-scripts.md and the AGENTS notes.

Tests: frontend/tests/testscripts.test.js - the option list/grouping, the
EF-only filter, the filter input, the pick->path fill and the form's
picker render for write and read.  1061 Python + 1071 frontend.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.37.0"
+version = "3.38.0"
 description = "HTTP REST server wrapping pysim for the SIMple PWA"
 license = { text = "GPL-2.0-or-later" }
 requires-python = ">=3.9"