feat: the Data Connection Status Change event gets its parameter form (0x1D)

EVENT_FORMS[0x1D] was missing, so its Send button posted event_data: null -
the ENVELOPE carried only the event list and device identities, none of the
event's data objects.  The form now builds the TS 31.111 7.5.25.2 object set
(tags per TS 101 220 / TS 31.111 9.3): data connection status (9D), connection
type (AA), optional (E/5G)SM cause (AE), transaction identifier (1C), optional
location information (13, CR flag 0 as the spec requires for this command),
optional access technology (BF), location status (9B), optional APN (C7) and
PDP/PDN/PDU type (0B).

Adjacent spec fixes found while verifying:
- the Access Technology Change options (0x0B) did not match the pinned
  TS 102 223 V18.3.0 8.61 coding (GSM Compact / GSM w-EGPRS / UTRAN w-HSDPA
  ...); they now use the shared ACCESSTECH list, whose two labels were also
  corrected (TIA/EIA-553-A, TIA/EIA-136-270);
- _send_event_download() wrote the D6 length as a single byte - a long APN
  would overflow it; 128..255 bytes now use the BER long form (81 <len>).

Tests: the 0x1D build (defaults, full form, fallbacks), the 8.61 option list,
the long-form D6.  Help EN/RU and both AGENTS files; sw cache simple-v342.

frontend/help.html

@@ -503,6 +503,7 @@
 		<li><strong>Location Status</strong> — dropdown: Normal / Limited / No service (tag <code class="font-mono text-sm">9B</code>)</li>
 		<li><strong>Access Technology Change</strong> — 13 RAT types (tag <code class="font-mono text-sm">BF</code>)</li>
 		<li><strong>Network Rejection</strong> — full adaptive form: registration type (LU / GPRS / EPS / 5GS), location fields (MCC, MNC, LAC, RAC, TAC), access technology, and a 53-cause unified rejection cause dropdown covering EMM, GMM, 5GMM and LU causes</li>
+		<li><strong>Data Connection Status Change</strong> (0x1D) &mdash; status (successful / rejected / dropped-deactivated), connection type (PDP / PDN / PDU), optional (E/5G)SM cause, transaction identifier and location status, plus optional access technology, APN, PDP/PDN/PDU type and location information (MCC/MNC + LAC + Cell ID) &mdash; TS 131 111 &sect;7.5.25</li>
 		<li><strong>Poll Interval Negotiation</strong> (0x1C) — proposes a poll interval as a Duration (unit + value); after sending, the UICC's answer is shown (accepted / rejected / modified + duration), and a <em>modified</em> duration becomes the background poll interval (TS 102 223 &sect;7.5.22). The form appears when the card subscribed to this event.</li>
 	</ul>
 	<p class="text-sm mb-3">Sending an event uses <code class="font-mono text-sm">ENVELOPE(Event Download)</code> per TS 102 223 / TS 131 111.</p>