Multi‑account view mode from a single main account

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### Is your feature request related to a problem?

Request to add a “multi‑account view” feature that allows a user to sign in with one main account and attach multiple sub‑accounts to it. The sub‑accounts are view‑only: they never initiate transactions and are used solely to view balances, stake, rewards, and activity.

- Many users manage multiple addresses (e.g., different wallets, custodial accounts, or accounts for family/clients).
- Currently, they must manually switch addresses or log in repeatedly to monitor each one.
- A main account with attached, view‑only sub‑accounts would make it much easier to monitor multiple addresses from one dashboard.

### Describe the solution you'd like

- User logs in / connects a wallet as the main account.
- From a “Manage watched accounts” or similar section, the user can:
- Add sub‑accounts by address (no signing needed for those addresses).
- Optionally label each sub‑account (e.g., “Treasury”, “Cold wallet 1”).

**The UI then shows:**

- A list of sub‑accounts with balances, stake, rewards, etc.
- Possibly an aggregate summary (total LPT, total stake, etc.) across all sub‑accounts.
- Sub‑accounts:
- Are never used to sign transactions.
- Do not have any write/interaction permissions.
- Are stored as watched addresses associated with the main account/browser profile.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

The issue names no files, tests, or entry points. Start by locating the account connection and dashboard entry points, then trace how balances, stake, rewards, and activity are loaded. Done means users can attach labeled, view-only addresses, see their data and any aggregate summary, and cannot use sub-accounts to sign transactions.

Written by the indexing model from the issue text.