🛡️ Sentinel: [CRITICAL] Fix arbitrary command execution via unvalidated bitcoin-cli path

[bitcoiner-dev]

🚨 Severity: CRITICAL
💡 Vulnerability: The bitcoin_cli parameter sourced from the user profile json was used directly as the target executable in std::process::Command::new(). While immune to bash shell injections like bitcoin-cli ; rm -rf /, it still allowed an attacker with file write access to the config to specify any system binary as the bitcoin_cli executable (e.g., /bin/sh, /usr/bin/python, or C:\Windows\System32\cmd.exe), which would then be executed with attacker-controlled arguments via the bitcoin_cli_args array.
🎯 Impact: Local arbitrary command execution.
🔧 Fix: Implemented validate_bitcoin_cli_path to strictly enforce that the provided path must:

1. Not contain directory traversal (..)
2. Be exactly bitcoin-cli or bitcoin-cli.exe
3. OR be an absolute path where the final executable name is exactly bitcoin-cli or bitcoin-cli.exe.
   ✅ Verification: cargo test --bin zinc-cli verifies the new path enforcement checks.

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PR created automatically by Jules for task 14179680337620087440 started by @bitcoiner-dev

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