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/modello-dati.md

@@ -826,8 +826,8 @@ senza riavviare (vedi [limiti-noti.md](limiti-noti.md)).
   [DAT-69], che scrivono la propria voce di audit.
   *Codice:* `app/api/routes/admin.py:pause_lottery` ·
   `app/api/routes/admin.py:resume_lottery` · *Test:* `tests/unit/test_admin.py`
-  *Stato:* da implementare (B-82, B-85) · *Oggi:* l'unica pausa automatica è
-  `resurrected_tx` (B-78); quelle di B-82 e B-85 non esistono ancora.
+  *Stato:* da implementare (B-82) · *Oggi:* le pause automatiche sono
+  `resurrected_tx` (B-78) e `reorg` (B-85); quella di B-82 non esiste ancora.
 
 - **[DAT-62]** `deposit_confirmations` (predefinito 6) è il numero di
   conferme dopo cui un output che paga un utente si accredita ([DAT-10]);
@@ -864,12 +864,12 @@ senza riavviare (vedi [limiti-noti.md](limiti-noti.md)).
   successivo.
   *Codice:* `app/api/routes/admin.py:pause_lottery` ·
   `app/api/routes/admin.py:resume_lottery` ·
-  `app/electrum/listener.py:ElectrumListener._apply_header` ·
+  `app/electrum/listener.py:ElectrumListener._record_reorg` ·
   `app/rounds/scheduler.py:RoundScheduler._trigger_payout` ·
-  `app/tx/reconcile.py:reconcile_once` · *Test:* `tests/unit/test_pause_reason.py`
-  *Stato:* da implementare (B-82, B-85, B-90) · *Oggi:* si scrivono solo
-  `operator` (`POST /admin/pause`) e `resurrected_tx` (il riconciliatore);
-  `reorg`, `payout_blocked` e `START_PAUSED` non hanno ancora chi li scrive.
+  `app/tx/reconcile.py:reconcile_once` · *Test:* `tests/unit/test_pause_reason.py`, `tests/unit/test_electrum_listener.py`
+  *Stato:* da implementare (B-82, B-90) · *Oggi:* si scrivono
+  `operator` (`POST /admin/pause`), `resurrected_tx` (il riconciliatore) e
+  `reorg` (il listener); `payout_blocked` e `START_PAUSED` non hanno ancora chi li scrive.
 
 - **[DAT-31]** Con `fee_address` vuoto (o di soli spazi) non si apre nessun round
   (B-66). Una volta impostato, l'API non permette di svuotarlo di nuovo: la