wallet: Pass `prevClientVersion` to `RemoteFeatureFlagController`

[grypez]

Problem

RemoteFeatureFlagController is constructed without a prevClientVersion argument. Without it the controller has no way to detect a version change, so its cached remote feature flags are never invalidated on upgrade — clients may run on stale flag values after updating.

Proposed direction

Add an optional prevClientVersion?: string field to WalletOptions and pass it through to the RemoteFeatureFlagController constructor. Consumers (e.g. wallet-cli) are responsible for supplying the previously-run version; omitting it preserves current behaviour.

Acceptance

• WalletOptions has an optional prevClientVersion field.
• The RemoteFeatureFlagController init passes prevClientVersion: options.prevClientVersion to the constructor.
• Existing tests pass.
• Changelog entry added.