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

[bitcoiner-dev]

🚨 Severity: CRITICAL
💡 Vulnerability: Path traversal vulnerability in src/commands/snapshot.rs. The SnapshotAction::Save and SnapshotAction::Restore commands allowed user-controlled name parameters to be passed directly to Path::join without validation. If an attacker specified an absolute path (e.g., /etc/passwd) or a relative traversal path (e.g., ../../../etc/passwd), Path::join would interpret it and write or read files outside the intended snapshot directory.
🎯 Impact: An attacker could read arbitrary local files by passing an absolute path to snapshot restore, effectively overwriting their profile with file contents, or overwrite arbitrary files by using snapshot save.
🔧 Fix: Implemented strict allowlist validation (crate::utils::validate_file_name) that ensures the snapshot name contains only alphanumeric characters, underscores, and dashes. This is called before path resolution in both snapshot actions.
✅ Verification: Verified using cargo test and cargo check. Evaluated the edge-case behavior of Path::join via a scratchpad test to ensure the path parsing works safely with the validation in place.

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PR created automatically by Jules for task 12334089060266422385 started by @bitcoiner-dev

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