fix(security): harden outbound destination validation

[Wikid82]

Summary

Hardens how Charon validates destinations for outbound requests by consolidating the address checks into one shared policy used by every caller, and tightening the defaults.

• Commit 1 and 2 are refactors with no behavior change (parity tests cover the old and new option sets).
• Commit 3 flips the defaults and removes the superseded options.
• Features that legitimately target overlay-network addresses (uptime checks, remote storage, webhooks, notification providers) keep working.
• No settings, schema, API, or UI changes.

Testing

• Unit tests for the shared policy, per-caller wiring, and boundary addresses.
• Backend build, full test run, lint, and coverage gates pass locally.

Claude Code was used to help produce this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

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📦 SBOM Summary

• Components: 1870

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🟢 Low	0
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