feat: convert capabilities to getter for subclass overrides

[mathieuartu]

Examples

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Note

Makes keyring capabilities dynamically overridable.

• Change KeyringWrapper.capabilities from a readonly property to a getter, enabling subclasses to compute capabilities at runtime
• Update QrKeyringV2 to override capabilities and return mode-specific capabilities (ACCOUNT vs HD) instead of redefining the property via Object.defineProperty
• Update changelogs for keyring-api and keyring-eth-qr to document the change

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