This introduce the UI flow to load a AssumeUTXO snapshot
into the Bitcoin Core App. It modifies the connection seetings
and adds a SnapshotSettings file, Icon, and modified profress
bar.

It has been rebased

        Adds minimal wiring to connect QML GUI to loading a signet UTXO snapshot via
        the connection settings. Uses SnapshotSettings.qml to allow user interaction.
	Modifies src/interfaces/node.h, src/node/interfaces.cpp
        and chainparams.cpp (temporarily for signet snapshot testing)
        to implement snapshot loading functionality through the node model.

        Current limitations:
        - Not integrated with onboarding process
        - Requires manual navigation to connection settings after initial startup
        - Snapshot verification progress is working, could be improved

        Testing:
        1. Start the node
        2. Complete onboarding
        3. Navigate to connection settings
        4. Load snapshot from provided interface