Add optional clean relay mode for unstable provider streams

[jake1164]

Child of #62.

Goal: provide a stabilization mode for providers that emit broken timestamps or incomplete H.264 context after reconnects.

Context:

• 2026-04-24 RCA points to upstream instability followed by FFmpeg missing PPS/SPS and DTS discontinuities.
• Existing HLS relay path already uses FFmpeg in src/M3Undle.Web/Streaming/Upstream/UpstreamStreamConnector.cs.

High-level ask:

• Add/configure an optional FFmpeg remux relay for live MPEG-TS provider streams.
• Generate/repair timestamps and resend headers where possible.
• Keep this opt-in or provider-scoped because it costs CPU and can add latency.