🛡️ Sentinel: [CRITICAL] Fix SSRF in APRS Poller TCP Connection

[d3mocide]

🚨 Severity: CRITICAL
💡 Vulnerability: SSRF was possible via the asyncio.open_connection(host, port) calls in the APRS poller (fetching config from the poller_sources DB table) and in the Beast and CoT receivers. An attacker with admin privileges could manipulate the configuration to probe and connect to arbitrary internal/private services on the backend network via the poller container.
🎯 Impact: This allowed connection to internal ports/services which could bypass firewalls, conduct network scans, or interact with unauthenticated internal applications.
🔧 Fix: Imported and invoked the centralized validate_safe_host method to ensure the target host resolves to a safe, public IP before initiating the socket connection.
✅ Verification: Ran the full backend and poller test suites to verify no breaking changes were introduced and code compiles successfully.

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PR created automatically by Jules for task 5105308995645511795 started by @d3mocide

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