feat: consolidate on the shadcn frontend and harden playback

Frontend
- Replace the Ant Design app with the shadcn/ui app as the single frontend,
  keeping the portfolio side-by-side revertible in this commit.
- Drop the abandoned mdui experiment and the AntD tree so there is one app,
  one router and one design system to maintain.

Live playback
- Stop racing the encoder. lowLatencyMode + liveSyncDurationCount:1 targeted a
  single 4s segment, so playback ran at up to 1.10x and the forward buffer
  bottomed out at 0.1s, re-buffering every segment. Measured over 40s:
  buffer min 0.1s -> 8.9s, rate 1.00 constant, 0 stalls.
- Remove the 落后 labels and the page-level edge-snapping timer that fought
  hls.js over two different definitions of "latency".
- Live can no longer be paused: the control is not rendered while it plays, so
  the icon can never misreport state.
- Fix autoplay: muted autoplay started silently and never unmuted, and the
  gesture that restored sound also toggled playback off. One owner now.

Source ("原画") rendition
- Publish the publisher's stream remuxed losslessly via -c:v copy alongside the
  transcoded ones, so a source option exists even when every ladder entry
  downsizes.
- Give renditions an ASCII path slug: the HLS path is part of the URL and
  MediaMTX rejects non-alphanumeric paths, so 原画 could never be served.

Backend
- Supervise MediaMTX from the backend: start it at boot and restart it on exit,
  never killing an origin it did not start.
- Clear stale HLS output before restarting an encoder; an ENDLIST-less playlist
  left by a dead encoder hangs hls.js forever.
- Mark JSON timestamps as UTC. utcnow().isoformat() emitted a naive string that
  JS read as local time, so every viewer heartbeat looked 8 hours old in UTC+8
  and the live board's active-viewer count was permanently zero.
- Rebind a viewer session when it arrives on another stream instead of failing,
  and survive the StrictMode double-heartbeat race on first insert.
- Replace the Linux-only /proc and os.getloadavg metrics with psutil.
- Complete MediaMTX's cookieCheck redirect inside /hls proxying, and hold the
  httpx client open for the streamed body.

Housekeeping
- Ignore RainOSS (it stores accessKeySecret), runtime output, TLS keys and
  .venv; remove generated screenshots, load test scripts and stray files.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

start.sh

@@ -1,44 +1,25 @@
 #!/bin/bash
-# StreamCore - Start all services
+# StreamCore - Start the backend.
+#
+# MediaMTX, the transcoders and the HLS tree are managed by the backend itself:
+# it starts the media origin at boot, supervises ffmpeg, and restarts either if it
+# dies. This script only has to bring up the process that owns all of that.
 set -e
 
 BASE="$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"
 
-echo "[StreamCore] Starting services..."
+export LS_HLS_RUNTIME_DIR="${LS_HLS_RUNTIME_DIR:-$BASE/runtime/hls}"
+export LS_REPLAY_MEDIA_DIR="${LS_REPLAY_MEDIA_DIR:-$BASE/runtime/replay}"
+mkdir -p "$LS_HLS_RUNTIME_DIR" "$LS_REPLAY_MEDIA_DIR" "$BASE/runtime/logs"
 
-# MediaMTX origin
-cd "$BASE/mediamtx"
-if pgrep -f "mediamtx mediamtx.yml" > /dev/null 2>/dev/null; then
-  echo "[StreamCore] MediaMTX already running."
-else
-  nohup ./mediamtx mediamtx.yml > /tmp/mediamtx.log 2>&1 &
-  sleep 2
-  echo "[StreamCore] MediaMTX started (RTMP :1935, HLS :8888, API :9997)."
-fi
+HOST="${LS_HOST:-0.0.0.0}"
+PORT="${LS_PORT:-8080}"
 
-# Backend API
 cd "$BASE/backend"
-if curl -sf http://127.0.0.1:8080/api/health > /dev/null 2>&1; then
-  echo "[StreamCore] Backend already running."
-else
-  (exec ./venv/bin/python run.py &) </dev/null &>/tmp/backend.log &
-  disown
-  sleep 3
-  echo "[StreamCore] Backend started on :8080."
-fi
+PY="$BASE/backend/venv/bin/python"
+[ -x "$PY" ] || PY="$BASE/backend/.venv/bin/python"
+[ -x "$PY" ] || PY="python"
 
-# Frontend
-cd "$BASE/frontend"
-if curl -sf http://127.0.0.1:5173 > /dev/null 2>&1; then
-  echo "[StreamCore] Frontend already running."
-else
-  (exec npm run dev &) </dev/null &>/tmp/frontend.log &
-  disown
-  sleep 3
-  echo "[StreamCore] Frontend started on :5173."
-fi
-
-echo "[StreamCore] All services up."
-echo "  Public:  http://nbd.rainplay.cn:13001/"
-echo "  Admin:   http://nbd.rainplay.cn:13001/admin/login"
-echo "  RTMP:    rtmp://nbd.rainplay.cn:13001/live/{key}"
+echo "[StreamCore] Starting backend on ${HOST}:${PORT}..."
+echo "[StreamCore] MediaMTX, transcoders and HLS are supervised by the backend."
+exec "$PY" -m uvicorn main:app --host "$HOST" --port "$PORT"