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/tests/event_forms.test.js

@@ -34,6 +34,8 @@ eval(extractFunc(html, 'cmdQualifierShort'));
 eval(extractBlock('const EVENT_NAMES = {', 'const REJECTION_CAUSES = [').replace(/^const /gm, 'var '));
 eval(extractBlock('const REJECTION_CAUSES = [', 'const EVENT_FORMS = {').replace(/^const /gm, 'var '));
 eval(extractBlock('const EVENT_FORMS = {', 'const PLI_QUALIFIERS = [').replace(/^const /gm, 'var '));
+eval(extractFunc(html, 'encPlmn'));
+eval(extractFunc(html, 'bytesToHex'));
 
 test('CMD_NAMES decodes timer management and the BIP commands', () => {
 	assert.strictEqual(CMD_NAMES['01'], 'REFRESH');
@@ -97,3 +99,28 @@ test('channel status event builds the B8 channel status TLV', () => {
 	assert.strictEqual(build({ channel: '1', state: '0', info: '0' }), 'B8020100');
 	assert.strictEqual(build({ channel: '0', state: '64', info: '0' }), 'B8024000');
 });
+
+test('the data connection status change event builds the 7.5.25 object set', () => {
+	const build = EVENT_FORMS[0x1D].build;
+	assert.strictEqual(EVENT_FORMS[0x1D].note, undefined);
+	// the four mandatory objects; every conditional object omitted
+	assert.strictEqual(build({ status: '0', type: '0', ti: '00', loc_status: '0' }),
+		'9D0100AA01001C01009B0100');
+	// full form: cause, location information, access technology, APN, type
+	assert.strictEqual(
+		build({ status: '1', type: '2', cause: '26', ti: '85', mcc: '250', mnc: '01',
+			lac: '00FF', cell: '0001', tech: '8', loc_status: '1', apn: 'internet', pdp_type: '3' }),
+		'9D0101AA0102AE011A1C0185130752F01000FF0001BF01089B0101C708696E7465726E65740B0103');
+	// an empty TI falls back to 00; the location defaults fill missing fields
+	assert.strictEqual(build({ status: '2', type: '1', ti: '', mcc: '250', loc_status: '2' }),
+		'9D0102AA01011C0100130752F010000000019B0102');
+});
+
+test('the access technology options follow the pinned 8.61 coding', () => {
+	const opts = EVENT_FORMS[0x0B].fields[0].opts;
+	assert.deepStrictEqual(opts.map(o => o.v), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]);
+	assert.strictEqual(opts[1].l, 'TIA/EIA-553-A');
+	assert.strictEqual(opts[2].l, 'TIA/EIA-136-270');
+	assert.strictEqual(opts[10].l, 'NG-RAN');
+	assert.strictEqual(opts[12].l, 'Satellite E-UTRAN');
+});