Export connections as CSV + audit trail for rule changes

[butterson1]

Missing features

• No way to export connection logs for external analysis
• No audit trail when rules are created/modified/deleted
• Retention policy (purge_days) is config-only, no UI

Solution

• GET /api/connections/export?format=csv endpoint
• Download button on Connections page
• rule_audit table tracking who changed what rule and when
• Retention settings in the UI (with manual purge button)