feat: modernize settings and add SOCKS5 support

- Split monolithic SettingsView.swift into modular Settings panes
- Add SOCKS5 proxy support to proxy configuration
- Fix ListRowDensity application in DownloadTable
- Improve discoverability of global speed limit by adding it to Downloads pane

Sources/Firelink/Settings/PowerSettingsPane.swift

@@ -0,0 +1,17 @@
+import SwiftUI
+
+struct PowerSettingsPane: View {
+    @EnvironmentObject private var settings: AppSettings
+
+    var body: some View {
+        Form {
+            Section {
+                Toggle("Prevent system sleep while downloads are active", isOn: $settings.preventsSleepWhileDownloading)
+                Text("The display may still turn off. Firelink only keeps macOS awake enough to finish active downloads.")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+            }
+        }
+        .formStyle(.grouped)
+    }
+}