docs: help/README catch up with v3.8.0; keyset-number wording; RU "пресет"

Documentation:
- help (§1/§3): the SCP80 tab is switched by three pills - the tab list and the
  section intro now name the TAR probe (RU "TAR-сканер"); §3.1/§3.2 describe the
  Keyset selector next to the preset selector (and that a successful PoR
  advances the counter only when SPI1 carries a counter check); §4 describes
  the keyset editor rows, the derived number and the per-keyset counters; the
  probe section keeps its counter rule.
- README/README_RUS: the SCP80 tab says three pills and gains a "TAR probe" /
  "TAR-сканер" section (standard list, verdicts, counter persistence); the
  Cards section is rewritten for the server-side store - keysets, server-owned
  per-keyset counters with the audit trail, JSON export/import as the migration
  path, the keyset editor, the equipped-card mismatch banner - and the field
  table, "Add a card" and "Edit / remove" follow.

Terminology:
- "key version" is no longer used for SCP80 keysets in the UI, the server error
  strings and the docs: the selector is "Keyset", its options "Keyset 1 - ...",
  the messages say "keyset N ...".  The TS 102 225 A.1/A.2 quotes and the GP
  PUT KEY P1 field keep the spec's own wording.
- RU keeps the word "keyset" untranslated ('Добавить keyset', 'Номер keyset',
  "не является keyset пресета", ...) and uses "пресет" instead of
  "предустановка" throughout the dictionary, the help and README_RUS.

sw cache simple-v340.  Tests: 742 Node / 619 Python.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v339';
+const CACHE = 'simple-v340';
 const URLS = [
   'index.html',
   'help.html',