🛡️ Sentinel: [HIGH] Fix insecure default file permissions for snapshot directory

[bitcoiner-dev]

🚨 Severity: HIGH
💡 Vulnerability: The CLI application creates sensitive snapshot data directories using std::fs::create_dir_all. This standard function creates directories using the system's default umask, which can allow other local users to read sensitive backup contents.
🎯 Impact: This could expose sensitive user data like wallets, mnemonic, config parameters and others to a local privilege escalation or exposure if the CLI is executed on a shared system.
🔧 Fix: We swapped std::fs::create_dir_all for crate::paths::create_secure_dir_all, which correctly configures explicit permissions (e.g. 0o700).
✅ Verification: cargo test runs correctly. cargo clippy and cargo fmt executed successfully and the security behavior of the directory creations was addressed.

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PR created automatically by Jules for task 2440586732785390127 started by @bitcoiner-dev

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