🛡️ Sentinel: [CRITICAL] Fix SSRF in remote CLI execution

[rschumann]

🚨 Severity: CRITICAL
💡 Vulnerability: Server-Side Request Forgery (SSRF) in cli_executor.go due to unvalidated REMOTE_COMMAND_HOST.
🎯 Impact: An attacker could abuse protocol schemes (e.g., file://) to access internal resources or execute arbitrary commands.
🔧 Fix: Added net/url to parse and strictly validate the URL scheme (http or https) before constructing the network request.
✅ Verification: Verified via gosec scan and running local unit tests (go test ./... -short).

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PR created automatically by Jules for task 7457658992822630952 started by @rschumann

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