fix(wallet-switch): cluster C — no mis-scoping in the unknown-identity window

From the audit: while a switch/first-load is in flight the wallet identity hash
is empty, so contact/portfolio scope-writes silently fell back to "global"
(leaking a wallet-specific entry into every wallet) and scope-filters showed
every wallet's scoped entries.

- Contacts: a NEW wallet-scoped contact created while the identity is unknown is
  now refused with a clear message (tick global or wait); editing an existing
  scoped contact preserves its scope instead of demoting it to global.
- Portfolio: the "Add group" button is disabled while the identity is unknown
  (with a tooltip), so a new group can't get an empty/global scope.
- Both views' visibility filters now show ONLY global entries when the identity
  is unknown — never another wallet's scoped contacts/groups — instead of
  showing everything.
- +2 i18n strings (8 langs; reworded one zh string to stay within the CJK subset).

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

res/lang/de.json

@@ -305,6 +305,7 @@
     "contact_global_tt": "Ein: Dieser Kontakt bleibt sichtbar, egal welche Wallet Sie laden. Aus: Er gehört nur zur aktuellen Wallet.",
     "contact_preview_addr": "Adresse erscheint hier",
     "contact_preview_name": "Kontaktname",
+    "contact_wallet_loading": "Die Wallet lädt noch — aktiviere „In jeder Wallet anzeigen“ oder versuche es gleich erneut.",
     "contacts": "Kontakte",
     "contacts_search_no_match": "Keine passenden Kontakte",
     "contacts_search_placeholder": "Kontakte durchsuchen...",
@@ -977,6 +978,7 @@
     "portfolio_style_featured": "Hervorgehobene Zeilen",
     "portfolio_style_label": "Portfolio-Stil",
     "portfolio_untitled": "Ohne Titel",
+    "portfolio_wallet_loading": "Warte, bis die Wallet fertig geladen ist, um eine Gruppe hinzuzufügen.",
     "price_chart": "Preisdiagramm",
     "privacy_great": "Großartige Privatsphäre!",
     "privacy_low": "Geringe Privatsphäre — Gelder abschirmen",