fix(contacts): stable per-wallet scope so contacts don't vanish (address-hash drift)

Contacts were scoped by activeWalletIdentityHash() — a hash of the wallet's
ENTIRE address set. Creating a new receive address grows the set, changing the
hash, so every contact stamped with the old hash falls out of the scope filter
(contacts_tab.cpp:915) while still being counted — the "3 saved, 1 showing"
symptom, where only the one set to global (which bypasses the scope) survives.
It also hid scoped contacts on every startup before the daemon connected (hash
empty until addresses load).

Introduce a stable per-wallet scope id: WalletIndexEntry.scopeId ("w:"+random
hex), generated once and persisted in the wallet index (keyed by wallet file),
never recomputed from the mutable address set — so creating addresses, locking,
or disconnecting never changes it. App::activeWalletScopeId() establishes it on
first use. Contacts now scope + filter on this instead of the drifting hash. The
tx-history-cache identity (the hash's real purpose) is untouched.

Recovery for already-orphaned contacts:
- AddressBook::reattachLegacyScopes() re-attaches non-global, non-"w:" contacts
  to the active wallet's stable id; run once when there's a single known wallet
  (unambiguous attribution). Idempotent.
- The scope filter fails OPEN for legacy scopes (multi-wallet case where recovery
  can't attribute them) so no contact is ever hidden; stable "w:" scopes still
  match strictly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/data/wallet_index.cpp

@@ -25,6 +25,7 @@ bool sameEntry(const WalletIndexEntry& a, const WalletIndexEntry& b)
     return a.fileName == b.fileName
         && a.displayName == b.displayName
         && a.walletIdentityHash == b.walletIdentityHash
+        && a.scopeId == b.scopeId
         && a.cachedBalance == b.cachedBalance
         && a.cachedAddressCount == b.cachedAddressCount
         && a.lastOpenedEpoch == b.lastOpenedEpoch
@@ -61,6 +62,7 @@ bool WalletIndex::load()
                 if (w.fileName.empty()) continue;
                 w.displayName = e.value("name", w.fileName);
                 w.walletIdentityHash = e.value("identity", "");
+                w.scopeId = e.value("scopeId", "");
                 w.cachedBalance = e.value("balance", -1.0);
                 w.cachedAddressCount = e.value("addresses", (long long)-1);
                 w.lastOpenedEpoch = e.value("lastOpened", (long long)0);
@@ -96,6 +98,7 @@ bool WalletIndex::save()
             e["file"] = w.fileName;
             e["name"] = w.displayName;
             e["identity"] = w.walletIdentityHash;
+            e["scopeId"] = w.scopeId;
             e["balance"] = w.cachedBalance;
             e["addresses"] = w.cachedAddressCount;
             e["lastOpened"] = w.lastOpenedEpoch;