Add auto-reconnect with exponential backoff

Sessions configured with auto-reconnect will automatically attempt to
re-establish the connection when unexpectedly disconnected. Uses
exponential backoff (1s, 2s, 4s, 8s... up to 30s) with a configurable
maximum number of attempts (default 5).

- New SessionReconnecting state with pulsing indicator in tab bar
- SSH and Telnet profiles gain autoReconnect and maxReconnectTries fields
- RAW protocol already had autoReconnect; now uses the shared mechanism
- CancelReconnect API to abort in-progress reconnection
- Frontend shows reconnect attempt notifications
- Profile editor exposes toggle and max attempts in Advanced/Reconnection

frontend/wailsjs/go/api/Service.d.ts

@@ -3,6 +3,8 @@
 import {models} from '../models';
 import {context} from '../models';
 
+export function CancelReconnect(arg1:string):Promise<void>;
+
 export function CheckForUpdates():Promise<Record<string, any>>;
 
 export function ClearSessionHistory(arg1:string):Promise<void>;