fix: port OmxEncoder safety fixes from upstream FrogPilot

- OMX_Init/OMX_Deinit managed per encoder instance lifecycle
- Proper error handling in constructor, encoder_open, encoder_close
- Null guards on done_out.pop() and handle in destructor
- Codec config written directly to codecpar (no codec_ctx)
- ffmpeg faststart remux on segment close
- Crash handler in dashcamd for diagnostics
- DashcamFrames param for live frame count in status window

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

common/params.cc

@@ -110,6 +110,7 @@ std::unordered_map<std::string, uint32_t> keys = {
     {"CurrentBootlog", PERSISTENT},
     {"CurrentRoute", CLEAR_ON_MANAGER_START | CLEAR_ON_ONROAD_TRANSITION},
     {"DashcamDebug", PERSISTENT},
+    {"DashcamFrames", PERSISTENT},
     {"DashcamShutdown", CLEAR_ON_MANAGER_START},
     {"DisableLogging", CLEAR_ON_MANAGER_START | CLEAR_ON_ONROAD_TRANSITION},
     {"DisablePowerDown", PERSISTENT},