v3.18.0: the semantic event action for test scripts

The other-applet batch: a test script can send the common event downloads
semantically instead of raw hex.

- events.py: server-side mirrors of the PWA's event forms for Location status
  (0x03), Access technology change (0x0B), Network rejection (0x12 - the
  LA/RA/TA object selected by the registration group, the extended EMM cause
  and the extended information object) and Data connection status change
  (0x1D - status/type/TI plus the optional cause, host-clock 8.39 date-time,
  location information, access technology, APN and PDP/PDN/PDU type).  Fields
  are validated before the run (a bad value is a script error, not a step
  failure); `src` overrides the device-identities source (default terminal,
  matching the Phone forms).
- The engine gains the `event` action kind; the runner builds and sends it.
  The PWA's action-kind list stays in sync (drift-guarded - the guard itself
  caught its own regex bug on the first run).
- Byte parity: the vectors are generated from the PWA's own builders and
  pinned in tests/test_events.py; the frontend suites assert the same values.
  PLMN and SCTS helpers are mirrored too.
- The Phone tab's event form shows the built "Event data (hex)" (updated as
  the fields change), so every event without a builder can be used through
  the raw `envelope` action.
- The test-step editor offers the event select + a JSON fields textarea;
  malformed JSON refuses the save with a clear message.
- docs/test-scripts.md (the semantic-event table, an event example, the
  format stamp), docs/api.md and help EN/RU updated.

Tests: 812 frontend + 717 Python; sw cache simple-v381.

docs/api.md

@@ -667,7 +667,9 @@ keysets, TARs and counters.  The inline `preset` form stays for external
 callers.
 
 **Action steps** (`type: "action"`): `kind` is `envelope` (`event`, `data`),
-`menu-select` (`item_id` 1-255, or `text` + `mode` `exact`/`contains` with an
+`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
 optional `case_sensitive` - 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,