feat(transport): Adaptive FEC (loss-rate driven)

[Yanstart]

Context

Current FEC uses static Reed-Solomon parameters. Satellite loss rates vary (rain fade, handovers). FEC should adapt automatically.

Requirements

• Monitor packet loss rate per connection
• Adjust FEC ratio dynamically (more redundancy when loss is high)
• Reduce FEC overhead when loss is low (terrestrial)
• Disable FEC entirely below threshold (e.g., <0.1% loss)
• Hot-reloadable base parameters

Implementation

1. Add loss rate tracker to quick-transport (EWMA)
2. Map loss rate → FEC ratio (configurable curve)
3. Adjust RS parameters in quick-fec at runtime
4. Emit metrics for FEC overhead ratio

Acceptance Criteria

• FEC increases with loss rate
• FEC disabled on clean links
• Measurable improvement vs static FEC on variable-loss scenarios
• No FEC overhead on terrestrial