v3.19.0 (review fixes): expose the menu-select Match case choice; doc/comment fixes

Review of 7250dbd:
- the step editor's menu-select form gains a Match case select
  (Case-insensitive (default) / Case-sensitive); the step summary flags a
  case-sensitive step with (case), the saved params carry
  case_sensitive: true only when chosen, and the docs say the editor
  authors the flag.
- docs/api.md: fix the 'with an optionally' grammar.
- the Variant-2 menu test's comment claimed a contains match while it is an
  exact one; a real contains leg is added ('ыбор' -> item 128).
- timeless rationale for the case-insensitive default; the format note now
  dates the change.
sw cache simple-v389 (index.html/help changed).
Tests: 821 frontend + 726 Python.

docs/api.md

@@ -670,9 +670,8 @@ callers.
 optional `src` - the device-identities source override),
 `event` (`event` name or hex + `fields`, optional `src` - the semantic event
 download for 0x03/0x0B/0x12/0x1D), `menu-select` (`item_id` 1-255, or `text` +
-`mode` `exact`/`contains` with an
-optionally `case_sensitive: true` for an exact-case match, case-insensitive by
-default - the text is resolved against the card's cached
+`mode` `exact`/`contains` (case-insensitive by default; `case_sensitive: true`
+forces an exact-case match) - the text is resolved against the card's cached
 SET UP MENU, which is refreshed whenever the card sends the menu), `file-write`
 (`path`, `data`, `mode` `auto`/`binary`/`record`, `record`), `file-read` (same,
 verifies `check.data`),