feat(ui): promote the address book to a Contacts sidebar tab

Phase 0b. The address book was buried in Settings behind a modal dialog.
Make it a first-class "Contacts" tab (which will also become the chat
roster), rendered inline in the main content area.

- New NavPage::Contacts (after History; ICON_MD_CONTACTS) +
  WalletUiSurface::Contacts. isUiSurfaceAvailable's `default: return true`
  shows it in BOTH variants; uiSurfaceNeedsWalletData's default keeps it
  usable before wallet data loads. All the touchpoints wired: NavPageSurface,
  GetNavIconMD, the app.cpp dispatch case, the app_network.cpp tracePageName
  case, and the `contacts` i18n label.
- New src/ui/windows/contacts_tab.{h,cpp}: RenderContactsTab lifts the
  toolbar + table + add/edit modal out of address_book_dialog, rendered in a
  BeginChild scroll region (peers_tab pattern) instead of an overlay; the
  add/edit form stays a modal layered over the tab. Reuses the existing
  address_book_* i18n keys and the dialogs.address-book schema.
- Delete address_book_dialog.{h,cpp}; remove its app.cpp render pump and the
  dead App::show_address_book_. The Settings "Address Book…" button now
  navigates to the tab (setCurrentPage) instead of opening the modal, so the
  Tools & Actions grid layout is untouched.
- CMake: swap the dialog sources for contacts_tab.

Behavior-preserving move; search/sort/keyboard/contrast land in 0d. Visual
check pending the per-theme screenshot sweep.

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

src/ui/sidebar.h

@@ -25,6 +25,7 @@ enum class NavPage {
     Send,
     Receive,
     History,
+    Contacts,
     // --- separator ---
     Mining,
     Market,
@@ -51,6 +52,7 @@ inline const NavItem kNavItems[] = {
     { "Send",      NavPage::Send,     nullptr,    "send",     nullptr     },
     { "Receive",   NavPage::Receive,  nullptr,    "receive",  nullptr     },
     { "History",   NavPage::History,  nullptr,    "history",  nullptr     },
+    { "Contacts",  NavPage::Contacts, nullptr,    "contacts", nullptr     },
     { "Mining",    NavPage::Mining,   "TOOLS",   "mining",   "tools"     },
     { "Market",    NavPage::Market,   nullptr,    "market",   nullptr     },
     { "Console",   NavPage::Console,     "ADVANCED","console",  "advanced"  },
@@ -78,6 +80,7 @@ inline wallet::WalletUiSurface NavPageSurface(NavPage page)
     case NavPage::Send:     return wallet::WalletUiSurface::Send;
     case NavPage::Receive:  return wallet::WalletUiSurface::Receive;
     case NavPage::History:  return wallet::WalletUiSurface::History;
+    case NavPage::Contacts: return wallet::WalletUiSurface::Contacts;
     case NavPage::Mining:   return wallet::WalletUiSurface::Mining;
     case NavPage::Market:   return wallet::WalletUiSurface::Market;
     case NavPage::Console:  return wallet::WalletUiSurface::Console;
@@ -103,6 +106,7 @@ inline const char* GetNavIconMD(NavPage page)
     case NavPage::Send:      return ICON_MD_CALL_MADE;
     case NavPage::Receive:   return ICON_MD_CALL_RECEIVED;
     case NavPage::History:   return ICON_MD_HISTORY;
+    case NavPage::Contacts:  return ICON_MD_CONTACTS;
     case NavPage::Mining:    return ICON_MD_CONSTRUCTION;
     case NavPage::Market:    return ICON_MD_TRENDING_UP;
     case NavPage::Console:   return ICON_MD_TERMINAL;