Propagate --hd-path to auth signers and alias resolution.

[fnando]

What

Propate the HD path, so auth signers and alias resolution is consistent all around.

Why

https://stellarfoundation.slack.com/archives/C06GHH10005/p1772940381744689

Known limitations

N/A

[Copilot]

Pull request overview

This PR ensures the CLI’s --hd-path option is applied consistently when resolving account aliases and when constructing signers for Soroban auth, so derived addresses/signatures come from the same HD index across the flow.

Changes:

• Thread hd_path: Option<usize> through UnresolvedScAddress::resolve so account alias resolution derives the correct address for the selected HD path.
• Use config.hd_path() when building signers (source signer + auth signer resolution) instead of always defaulting to path 0.
• Add an integration test asserting --hd-path affects both --addr alias resolution and auth signing.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
cmd/soroban-cli/src/config/sc_address.rs	Adds hd_path parameter to address/alias resolution and uses it when deriving the account ID from an identity key.
cmd/soroban-cli/src/config/mod.rs	Propagates --hd-path into source_signer() so source auth signing uses the selected HD path.
cmd/soroban-cli/src/commands/contract/arg_parsing.rs	Propagates --hd-path into --addr resolution and auth signer derivation.
cmd/crates/soroban-test/tests/it/integration/hello_world.rs	Adds an integration test covering --hd-path propagation for auth invocation with --addr alias.