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]>

backend/routes/settings_route.py

@@ -2,6 +2,7 @@ import os
 import shutil
 from pathlib import Path
 
+import psutil
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel, Field
 from typing import Optional
@@ -88,33 +89,27 @@ async def update_transcode_profiles(
 
 @router.get("/system-metrics")
 async def get_system_metrics(_: bool = Depends(require_auth)):
-    load_1m, load_5m, load_15m = os.getloadavg()
-    memory_total = 0
-    memory_available = 0
-    meminfo = Path("/proc/meminfo")
-    if meminfo.exists():
-        values = {}
-        for line in meminfo.read_text(encoding="ascii").splitlines():
-            key, _, value = line.partition(":")
-            if value:
-                values[key] = int(value.strip().split()[0]) * 1024
-        memory_total = values.get("MemTotal", 0)
-        memory_available = values.get("MemAvailable", 0)
+    cpu_count = os.cpu_count() or 1
+
+    # There is no load average on Windows: os.getloadavg does not exist there, and
+    # psutil's emulation reads as 0.0 until its background sampler warms up (and
+    # never means quite the same thing). Report real CPU utilisation instead, so
+    # the dashboard's "CPU 使用率" card is not permanently stuck at zero.
+    if hasattr(os, "getloadavg"):
+        load_1m, load_5m, load_15m = os.getloadavg()
+        load_percent = round(min(100, load_1m / cpu_count * 100), 1)
+    else:
+        load_1m = load_5m = load_15m = None
+        # interval=None never blocks; it measures since the previous call anywhere
+        # in the process, which the supervisor's 10s metrics tick keeps fresh.
+        load_percent = round(psutil.cpu_percent(), 1)
+
+    memory = psutil.virtual_memory()
+    network = psutil.net_io_counters()
 
     metrics_path = Path(settings.replay_media_dir).resolve()
     disk_path = metrics_path if metrics_path.exists() else Path.cwd()
     disk = shutil.disk_usage(disk_path)
-    cpu_count = os.cpu_count() or 1
-    network_in_bytes = 0
-    network_out_bytes = 0
-    netdev = Path("/proc/net/dev")
-    if netdev.exists():
-        for line in netdev.read_text(encoding="ascii").splitlines()[2:]:
-            _, _, counters = line.partition(":")
-            fields = counters.split()
-            if len(fields) >= 9:
-                network_in_bytes += int(fields[0])
-                network_out_bytes += int(fields[8])
 
     return {
         "cpu": {
@@ -122,12 +117,13 @@ async def get_system_metrics(_: bool = Depends(require_auth)):
             "load_1m": load_1m,
             "load_5m": load_5m,
             "load_15m": load_15m,
-            "load_percent": round(min(100, load_1m / cpu_count * 100), 1),
+            "load_percent": load_percent,
+            "percent": load_percent,
         },
         "memory": {
-            "total": memory_total,
-            "available": memory_available,
-            "used_percent": round((1 - memory_available / memory_total) * 100, 1) if memory_total else 0,
+            "total": memory.total,
+            "available": memory.available,
+            "used_percent": round((1 - memory.available / memory.total) * 100, 1) if memory.total else 0,
         },
         "disk": {
             "total": disk.total,
@@ -135,7 +131,7 @@ async def get_system_metrics(_: bool = Depends(require_auth)):
             "used_percent": round(disk.used / disk.total * 100, 1) if disk.total else 0,
         },
         "network": {
-            "bytes_recv": network_in_bytes,
-            "bytes_sent": network_out_bytes,
+            "bytes_recv": network.bytes_recv,
+            "bytes_sent": network.bytes_sent,
         },
     }