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/preload/preload.ts

@@ -3,6 +3,7 @@ import {
   AddLinksPayload,
   AppSettings,
   DuplicatePolicy,
+  SessionStats,
   StartConflictEntry,
   StartConflictResolutionResult,
   UiSnapshot,
@@ -40,6 +41,7 @@ const api: ElectronApi = {
   toggleClipboard: (): Promise<boolean> => ipcRenderer.invoke(IPC_CHANNELS.TOGGLE_CLIPBOARD),
   pickFolder: (): Promise<string | null> => ipcRenderer.invoke(IPC_CHANNELS.PICK_FOLDER),
   pickContainers: (): Promise<string[]> => ipcRenderer.invoke(IPC_CHANNELS.PICK_CONTAINERS),
+  getSessionStats: (): Promise<SessionStats> => ipcRenderer.invoke(IPC_CHANNELS.GET_SESSION_STATS),
   onStateUpdate: (callback: (snapshot: UiSnapshot) => void): (() => void) => {
     const listener = (_event: unknown, snapshot: UiSnapshot): void => callback(snapshot);
     ipcRenderer.on(IPC_CHANNELS.STATE_UPDATE, listener);