Summary

This PR updates hw-ledger transport lifecycle handling in two places:

• close/reset the active transport when a withApp operation fails
• add an explicit disconnect() method on Ledger and LedgerGeneric so consumers can clean up intentionally

Why

While testing extension flows, I kept hitting transport/session problems after failures and across hook lifecycles:

• if an operation fails, keeping the same app/transport around can cause follow-up errors and inconsistent state
• consumers need a reliable way to release an active transport during lifecycle transitions (unmount, refresh, replacing an instance)

Related context:

• Can't sign with Ledger or import Ledger account extension#1610
• Improve Ledger reliability and signing (WebHID, lifecycle, mismatch guard) extension#1611

Behavior:

• on withApp error: best-effort transport.close(), clear cached app, rethrow original error
• disconnect(): explicit consumer API to close an active transport without waiting for an internal failure path

Why disconnect() is needed

In useLedger-style flows, one hook instance can unmount while its transport is still open.
The next instance may then fail with “already open” transport errors.
disconnect() gives consumers a clean, explicit teardown point to avoid that.

Compatibility / risk

• error-path behavior is intentionally stricter: failed operations now reset transport state instead of leaving a possibly bad session alive