v3.18.1: the raw envelope action takes the source override too

The events without a semantic builder (MT call, IMS registration, slices, ...)
are network-sourced, but the raw `envelope` action had no `src` override - the
only way to express them was the semantic set.  `envelope` now accepts
`src` (82 terminal / 83 network) exactly like the `event` action; the step
editor exposes it and the authoring guide gets the row.

Also: the guide marks `por` as SCP80-only (the normaliser refuses it
elsewhere) and the semantic-events section names the shared src override.

Tests: 813 frontend + 717 Python; sw cache simple-v382.

pysim_simple_server/server.py

@@ -34,7 +34,7 @@ from osmocom.tlv import BER_TLV_IE
 from osmocom.utils import rpad
 
 
-VERSION = '3.18.0'
+VERSION = '3.18.1'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE
 
@@ -5953,7 +5953,7 @@ def _test_run_action(server, step, ctx):
     if kind == 'envelope':
         data, sw = _send_event_download(scc, p['event'],
                                         bytes.fromhex(p['data']) if p['data'] else None,
-                                        drain=False)
+                                        drain=False, src=p.get('src'))
         sent = 'ENVELOPE(Event Download) type=0x%02X' % p['event']
     elif kind == 'event':
         # The semantic event download: the builder owns the byte layout.