ui: FPLMN manual-selection clear and duplicate guard (v2.7.19)

Attaching to a PLMN listed in EF.FPLMN used to write successful locations
anyway, i.e. it attached to a forbidden network.  Per TS 23.122 a
successful manual selection removes the entry, so the attach scenarios
clear it first:

- netsim.remove_fplmn() clears every occurrence of the PLMN (entries are
  not compacted; FFFFFF gaps stay); insert_fplmn() returns None when the
  PLMN is already listed, so roaming_denied no longer stores duplicates
  (the live card had '250-99, 250-99').
- clear_fplmn() step, called from write_real_locations() -> covers
  attach_eps, attach_2g and the sms_received location rewrite; the write
  is logged as a normal fplmn update_binary.
- tests: remove_fplmn duplicates/absent/gaps; roaming_denied duplicate
  skip; attach clears both occurrences before the location writes;
  make_runner now copies FakeFileInfo so seeded data does not leak
  between tests.
- help EN/RU and AGENTS updated.

pysim_simple_server/server.py

@@ -26,7 +26,7 @@ from osmocom.tlv import BER_TLV_IE
 from osmocom.utils import rpad
 
 
-VERSION = '2.7.18'
+VERSION = '2.7.19'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE