🛡️ Sentinel: [CRITICAL] Fix path traversal in profile and snapshot paths

[bitcoiner-dev]

🚨 Severity: CRITICAL
💡 Vulnerability: The application constructed file paths for profiles and snapshots without sanitizing the profile_name or snapshot_name variables, allowing path traversal (e.g., via ../../).
🎯 Impact: An attacker or malicious configuration could cause the application to read, write, or overwrite arbitrary files on the filesystem.
🔧 Fix: Implemented validate_file_name in src/utils.rs to enforce an allowlist of characters (alphanumeric, underscores, and dashes) and applied this validation to config.profile and snapshot name arguments. Removed an insecure directory creation call in snapshot.rs since snapshot_dir() handles it securely.
✅ Verification: cargo test passes. Running with an invalid profile name (e.g., --profile ../../root) will immediately error out with Invalid input.

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PR created automatically by Jules for task 1542657143684160733 started by @bitcoiner-dev

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