feat: answer GET INKEY / GET INPUT interactively (v3.6.38)

The menu chain paused only for DISPLAY TEXT / SELECT ITEM / SET UP MENU,
so a GET INPUT was auto-answered with a bare success TR and no Text
string - the live RemMobileID PIN prompt got an empty answer.

Server: _parse_get_inkey/_parse_get_input read the prompt, qualifier
flags (digits-only, UCS2, Yes/No, immediate, hidden, packed, help),
Response length 91 and Default Text 9D; the fetch handler pauses with
them; _menu_send_response(..., text=) validates the answer (digits set,
min/max, one char for GET INKEY) and builds the Text string TLV 8D in the
requested coding (SMS unpacked 04 / UCS2 08 / packed 00 via _pack_gsm7),
Yes/No as 01/00, empty input as the null text string, help as result 13
and the variable-timeout Duration echoed (6.8.4).  /api/menu-respond
takes text; /api/stk-status carries pending_data so a card-initiated
prompt opens the panel; _decode_cmd decodes both commands.

PWA: stkInputHtml/stkInputHint/stkInputValidate render the constrained
panel (password field for hidden entry, numeric keyboard, default text,
Yes/No buttons, help, immediate-digit auto-submit); OK submits through
stkMenuOk; the poll opens the panel for card-initiated prompts.

sw cache simple-v311; tests: 517 Python / 674 Node.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v310';
+const CACHE = 'simple-v311';
 const URLS = [
   'index.html',
   'help.html',