Add direct private key login option (UserWallet-style)

[Stephen-Thomson]

Description of Changes

• Adds a third login option ("I prefer to manage my private key directly") using SimpleWalletManager with a disabled PrivilegedKeyManager — no password step, no recovery key, no profiles
• Renames the "Presentation Key" config section to "Wallet Login Type" with three options: WAB, direct key, and mnemonic presentation key (advanced)
• Ports deriveKeyMaterialFromMnemonic utility from the user-wallet repository for mnemonic-to-key derivation in direct-key mode
• The direct key login flow presents a single step with toggle between mnemonic phrase and hex private key input, plus random generation for both
• Login type persists in snapshots with backward compatibility for existing useWab boolean snapshots

Linked Issues / Tickets

None

Testing Procedure

Manually tested

• I have added new unit tests
• All tests pass locally
• I have tested manually in my local environment

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have updated CHANGELOG.md with my changes
• I have run npm run doc and npm run lint one final time before requesting a review
• I have fixed all linter errors to ensure these changes are compliant with ts-standard
• I have run npm version patch so that my changes will trigger a new version to be released when they are merged