🛡️ Sentinel: [CRITICAL] Fix command injection vulnerability in external binary execution

[bitcoiner-dev]

🚨 Severity: CRITICAL
💡 Vulnerability: Command injection / arbitrary code execution via configuration profile manipulation. If an attacker gains write access to profile.json, they could change bitcoin_cli to another system executable (e.g., rm, curl, bash), allowing them to execute arbitrary code.
🎯 Impact: High. An attacker could completely compromise the host system using "Living off the Land" techniques.
🔧 Fix:

1. Added validation in src/utils.rs run_bitcoin_cli to strictly enforce that the executing binary's file name is bitcoin-cli or bitcoin-cli.exe. This allows absolute paths (e.g. /usr/local/bin/bitcoin-cli) while ensuring safety.
2. Removed an unused duplicate of run_bitcoin_cli from src/wallet_service.rs to enforce centralization and prevent developers from accidentally using an unvalidated execution path.
   ✅ Verification: Ensure the test suite passes, cargo check and cargo clippy succeeds, and that using an invalid binary name via the configuration profile throws an error.

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PR created automatically by Jules for task 18227969967410617778 started by @bitcoiner-dev

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