Support multiple hardware wallets connected at once

**What problem are you trying to solve?**
I have multiple hardware wallets, and use multiple derivation paths within each hardware wallet. I want to be able to connect each of the hardware wallets/derivation paths to MetaMask and label them appropriately, without them getting deleted.

**Describe the solution you'd like**
When I connect a new hardware wallet, the previous one doesn't get deleted.

**Additional context**
Beyond just being able to sign with multiple hardware wallets without having to go through the connect process each time, retaining them with labels means I can transfer assets between them using the MetaMask UI without having to write down the address of each and manually verify. I can just choose destination from my list of wallets.

The issue does not name files, tests, or entry points. Start by locating the hardware-wallet connection and account-persistence flow in the TypeScript extension, then trace how multiple derivation paths are stored and labeled. Done means multiple connected wallets remain available in the UI and can be selected as transfer destinations without reconnecting.

Written by the indexing model from the issue text.