Add bandwidth statistics tab with live chart

- Add new Statistics tab between Downloads and Settings
- Implement real-time bandwidth chart using Canvas (60s history)
- Add session overview with 8 stats cards (speed, downloaded, files, packages, etc.)
- Add provider statistics with progress bars
- Add getSessionStats IPC endpoint
- Support dark/light theme in chart rendering

src/shared/preload-api.ts

@@ -2,6 +2,7 @@ import type {
   AddLinksPayload,
   AppSettings,
   DuplicatePolicy,
+  SessionStats,
   StartConflictEntry,
   StartConflictResolutionResult,
   UiSnapshot,
@@ -35,6 +36,7 @@ export interface ElectronApi {
   toggleClipboard: () => Promise<boolean>;
   pickFolder: () => Promise<string | null>;
   pickContainers: () => Promise<string[]>;
+  getSessionStats: () => Promise<SessionStats>;
   onStateUpdate: (callback: (snapshot: UiSnapshot) => void) => () => void;
   onClipboardDetected: (callback: (links: string[]) => void) => () => void;
   onUpdateInstallProgress: (callback: (progress: UpdateInstallProgress) => void) => () => void;