feat(ui): in-app FAQ, DPI-scaling audit fixes, mining/stratum polish + localize strings

Bundles the session's UI work (the touched files carry several of these
changes together, so they are committed as one coherent UI batch):

- FAQ: new RenderFaqDialog + data-driven faq_content, opened from a
  status-bar "?" (and the Windows title bar), styled like the Wallets
  modal with search, Wallet/Daemon tabs, and smooth scroll.
- DPI/font-scale audit: multiply hand-drawn absolute geometry by
  Layout::dpiScale() across ~30 files so nothing renders native-size at
  HiDPI / font_scale 1.5 (verified with a full sweep at 1.5x).
- Mining: chart now fills the horizontal space; thread stepper +/- buttons
  match the input-box height; move the stratum-host toggle into
  Node & Security (v1.3.0+).
- Settings: fix the auto-shield status text overlapping the grid.
- Sidebar: drop the peer-count badge on the Network button.
- i18n: wrap 193 hardcoded literals with TR() (keys/translations added in
  the preceding i18n commit), so the security/PIN/lock flow, seed-backup
  wizard, and witness-rebuild dialog localize.

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

src/ui/windows/key_export_dialog.cpp

@@ -173,7 +173,7 @@ void KeyExportDialog::render(App* app)
                             s_key = found;
                             s_show_key = wantViewing;  // viewing keys are less sensitive
                         } else {
-                            s_error = r.ok ? std::string("Key not available for this address") : r.error;
+                            s_error = r.ok ? std::string(TR("grpc_key_not_available")) : r.error;
                         }
                         wallet::secureWipeLiteSecret(found);
                         s_fetching = false;
@@ -240,14 +240,15 @@ void KeyExportDialog::render(App* app)
             ImGui::TextDisabled("%s", TR("key_export_click_retrieve"));
         } else {
             // Key fetched. Layout: [ key text (click-to-copy) + Show/Hide below ]  [ QR | square ].
-            const float gap   = 12.0f;
+            const float dp    = Layout::dpiScale();
+            const float gap   = 12.0f * dp;
             const float avail = ImGui::GetContentRegionAvail().x;
             // Larger, responsive QR: ~30% of the content width, clamped to a comfortable range.
             float qrSize = avail * 0.30f;
-            if (qrSize < 200.0f) qrSize = 200.0f;
-            if (qrSize > 340.0f) qrSize = 340.0f;
+            if (qrSize < 200.0f * dp) qrSize = 200.0f * dp;
+            if (qrSize > 340.0f * dp) qrSize = 340.0f * dp;
             float keyW = avail - qrSize - gap;
-            const bool sideBySide = keyW >= 200.0f;   // too narrow -> stack the QR under the key
+            const bool sideBySide = keyW >= 200.0f * dp;   // too narrow -> stack the QR under the key
             if (!sideBySide) keyW = avail;
 
             // Chunk for readability, but keep a Bech32 HRP (e.g. "secret-extended-key-main") intact