fix: chown helper socket to staff and verify readiness via socket ping

[naufaldi]

What Change

• Configure the privileged helper Unix socket with root:staff ownership and 660 permissions after creation
• Replace file-existence polling with a socket connectivity check when waiting for helper readiness after install/reconnect
• Surface the last socket ping error when helper readiness times out
• Add unit tests for helper socket group naming and readiness retry logic
• Bump Homebrew cask to v0.1.0-beta.3 with updated SHA256

Why Change

• GUI users in the staff group could not connect to the helper socket when it was only mode-restricted without group ownership
• Checking that the socket file exists did not guarantee the daemon was accepting connections
• The beta.3 release bundles the helper socket access fix for distribution via Homebrew

Impact

• Affected areas: fanguard-helper daemon, helper install/reconnect flow in commands.rs, Homebrew cask
• Breaking changes: No
• Dependencies: None
• Testing: cargo test helper — 4 tests passed

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