🛡️ Sentinel: [CRITICAL] Fix path traversal in snapshot commands

[bitcoiner-dev]

🚨 Severity: CRITICAL
💡 Vulnerability: Path Traversal in the Snapshot commands. The application was interpolating a user-supplied string (name) directly into snap_dir.join(format!("{name}.json")). Without validation, passing absolute paths (e.g. /etc/passwd) or relative upward traversals (e.g. ../../../some-file) caused Path::join to escape the intended snap_dir boundary. This permitted arbitrary file read (during Restore) and arbitrary file overwrite (during Save) with application permissions.
🎯 Impact: An attacker could craft a malicious payload (via the CLI argument for a snapshot name) to either read out arbitrary file data (exposing sensitive files like configurations or key material) or overwrite files on the system, leading to privilege escalation or complete system compromise in automated environments.
🔧 Fix: Implemented validate_file_name in src/utils.rs which applies a strict allowlist constraint on file name parts (alphanumeric, -, and _). Intercepted user input in SnapshotAction::Save and SnapshotAction::Restore and applied this validation prior to path joining. Added rigorous unit tests.
✅ Verification: Run cargo test --bin zinc-cli to ensure the validation logic correctly rejects inputs containing ../ or / separators, and ensures existing Save and Restore operations remain fully functional.

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PR created automatically by Jules for task 12040537447863696327 started by @bitcoiner-dev

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