refactor: delegate wallet state to Accounts SDK

[gakonst]

Summary

• load and persist ~/.tempo/wallet/store.json through the Accounts SDK CLI provider and filesystem storage
• select and hydrate payment access keys through the Accounts SDK access-key manager
• retain wallet-cli ownership only for one-time legacy keys.toml migration
• remove wallet-cli tests for the Accounts SDK private JSON parser and retain integration and migration coverage

Validation

• node --import tsx scripts/changelog.ts validate
• vp lint
• vp fmt --check
• tsc -b --noEmit
• tsc -p tsconfig.test.json --noEmit
• vitest run (116 tests)

The PR contains one signed commit.