release: v3.9.0 - the operation start buttons wait for a preset and a keyset

Gating: the SCP80 "Send to Card", the RAM Execute and the TAR-probe Execute
buttons carry `data-needs-keyset`; pysimApplyAvailability() disables them
(with the hint "Select a card preset and its keyset" when the card itself is
fine) unless the view's preset is selected and the form's keyset number is one
of its keysets - `spKeysetStartReady`, the same rule the click-time guards
enforce, which stay as the last line of defence.  spKeysetSync() refreshes the
gate on every preset/keyset change, and the KIc/KID index selects now call
spKeysetSync() so the keyset selector follows a manual index change too.

Version 3.9.0: server VERSION, pyproject.toml and the PWA header; sw cache
simple-v346; the workspace AGENTS gains its v3.9.0 history entry.

Tests: indicator.test.js drives the gate (no preset -> disabled with the hint,
an undefined keyset -> disabled, a matching keyset -> enabled) and guards the
three buttons' attribute; the cards/keysets/ram sandboxes stub
pysimApplyAvailability.  Help EN/RU notes the disabled start buttons.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v345';
+const CACHE = 'simple-v346';
 const URLS = [
   'index.html',
   'help.html',