Follow and record chain reorganisations, pausing on deep ones (B-85, ELC-09, ELC-22, ELC-23, ELC-24, AUD-38, DAT-69)

A reorganisation was neither recorded nor acted upon, and a competing header at the tip's
own height was ignored for as long as the tip stood, leaving the listener on an orphan.

- A header at the height we hold with a different hash is followed through the same
  fork-point search as any other reorg (ELC-09) instead of being ignored; it still has to
  bring valid work and a connected chain.
- ElectrumListener._record_reorg writes `chain_reorg_detected` (depth, fork height, old and
  new tip height and hash) before the window moves, so a failed write ends the session and
  the next server's announcement of the same fork is recorded then. Depth 1 is a
  transaction of its own; depth >= 2 also pauses the lottery with paused_reason 'reorg'
  and writes `lottery_paused` in the same transaction (begin_immediate first).
- Docs: ELC-09/22/23/24, AUD-03/11/38, DAT-30/69, OPS-30, RND-04, ADR-26/52 lose their
  B-85 "da implementare" lines.

Tests changed because the spec changed: test_apply_header_ignores_a_competing_header_at_
the_current_tip_height encoded the B-64 behaviour that ELC-09 now reverses; it is replaced
by test_a_competing_header_at_the_tip_height_is_a_reorg_to_follow and the depth tests.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/sicurezza.md

@@ -92,8 +92,8 @@ Restano **accettati**, e descritti in
   riorganizzazioni con pausa sopra la profondità 1 e verifica delle monete
   del round prima del pagamento ([ADR-52](adr/ADR-52-riorganizzazioni-catena-contengono-invece-ignorarle.md), B-82,
   B-85). Il denaro che un attaccante riesce a sottrarre è perso per la
-  piattaforma. *Oggi:* depositi a 1 conferma, nessuna riorganizzazione
-  rilevata, nessuna verifica prima del pagamento.
+  piattaforma. *Oggi:* depositi a 1 conferma e nessuna verifica prima
+  del pagamento (B-82); le riorganizzazioni sono rilevate e, da profondità 2, mettono in pausa.
 
 ## Inventario dei segreti