Sub-Issue 1: Shared Native Script Parsing Utilities

[Andre-Diamond]

Problem: Script parsing helpers exist in src/utils/validateMultisigImport.ts but are not shared with wallet building.

Tasks:

• Extract reusable helpers (decode native script CBOR, detect script type, compute required signers, collect sig key hashes, detect hierarchical wrappers) into a shared module.
• Document behavior for nested all/any/atLeast scripts, especially wrappers with a single child.

Affected files:

• src/utils/validateMultisigImport.ts
• src/utils/common.ts
• New shared utility (e.g. src/utils/nativeScript.ts)

Acceptance:

• Shared helpers can parse the example script and return required=2, type=atLeast, isHierarchical=true.
• No change in existing import validation behavior.