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.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v221';
+const CACHE = 'simple-v222';
 const URLS = [
   'index.html',
   'help.html',