iPad: hardware keyboard, pointer, and a camera-free pairing path (Phase 3)

Make the remote feel native with a Magic Keyboard / trackpad, and give iPad a
pairing path that survives a blocked camera.

Keyboard shortcuts (mirroring the Mac's .commands):
- Cmd+Return sends in the session follow-up composer and the start-chat composer
  (plain Return stays a newline in the multiline fields).
- On the approval card, Return allows and Esc denies -- the approval bar replaces
  the composer, so Return is unclaimed there. Allow stays gated on the biometric.

Pointer:
- .hoverEffect on the diff file-list rows (native List rows already hover).

Camera-free pairing (ManualPairingView):
- "Enter code manually" in both the pairing intro and Settings opens a sheet to
  paste the Mac's nucleic://pair?d=... code, parsed with the same
  PairingPayload(qrString:) the scanner uses (+ a Paste-from-clipboard button).
  The iPad scanner can't run while mirrored to an external display or in some
  Stage Manager states; this always works.

Note: the Mac's RemoteAccessView currently shows only the QR, so a follow-up host
change is needed to surface a copyable pairing link for this to be end-to-end.

Builds clean.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -223,6 +223,9 @@ struct SessionDetailView: View {
                                 .font(.title2)
                         }
                         .disabled(draft.trimmingCharacters(in: .whitespaces).isEmpty || !store.connectivity.isLive)
+                        // Hardware-keyboard send (Magic Keyboard on iPad), mirroring the Mac —
+                        // plain Return stays newline in the multiline field.
+                        .keyboardShortcut(.return, modifiers: .command)
                     }
                 }
             }
@@ -408,6 +411,7 @@ private struct SplitDiffView: View {
                             .contentShape(Rectangle())
                     }
                     .buttonStyle(.plain)
+                    .hoverEffect(.highlight)
                 }
                 if diff.truncated { TruncatedPatchNote().padding(12) }
             }