Restructure step 5: one media pipeline on a player host

- PlayerHost port (MediaKitHost): players by role, pins, hwdec policy,
  render probe, log routing, disposal order; the only media_kit user.
- MediaPipeline: plan (one pure switch over state, origin, caps,
  presence) -> resolve -> open (prepared player promoted, else fresh)
  -> ready; commands queued during a switch apply once (P15); viewers
  play the buffer and wait for a dropped source without seek loops (D6).
- Every web page resolved by our yt-dlp into an EDL with headers and
  cookies (danmaku excluded); mpv's ytdl_hook no longer used (ytdl=no).
- D11: sign-in errors say which cookies were used and whether they hold
  any for the site.
- Relay: 256 KiB slices read as they fill, superseded pulls released
  (seek-to-play ~4.2 s -> ~2.8 s, P29); own Jellyfin relay channel only
  when someone needs it (P28).
- STARSYNC_SMOKE run and a Windows CI smoke step after the build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tool/smoke_linux.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# The close smoke run of tool/smoke_windows.ps1 on Linux (the same app
+# mode, apps/desktop/lib/src/platform/smoke.dart): start the release
+# bundle with a short clip, open it, play, close; check it exited within
+# LIMIT seconds and left no process. Needs a display (skips without one).
+# Usage (after `flutter build linux --release`): tool/smoke_linux.sh [LIMIT]
+set -euo pipefail
+LIMIT="${1:-45}"
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+EXE="$ROOT/apps/desktop/build/linux/x64/release/bundle/starsync"
+[[ -x "$EXE" ]] || { echo "build first: $EXE missing" >&2; exit 1; }
+if [[ -z "${DISPLAY:-}${WAYLAND_DISPLAY:-}" ]]; then echo "skipped: no display"; exit 0; fi
+WORK="$(mktemp -d)"; trap 'rm -rf "$WORK"' EXIT
+MEDIA="$WORK/smoke.mp4"
+ffmpeg -y -v error -f lavfi -i testsrc2=size=320x180:rate=24 -f lavfi -i sine=frequency=440 \
+  -t 5 -c:v libx264 -preset ultrafast -pix_fmt yuv420p -c:a aac "$MEDIA"
+OUT="$WORK/smoke.txt"
+start=$(date +%s)
+STARSYNC_PROFILE=smoke STARSYNC_SMOKE="$MEDIA" STARSYNC_SMOKE_OUT="$OUT" "$EXE" >"$WORK/stdout.txt" 2>&1 &
+pid=$!
+exited=0
+for _ in $(seq $((LIMIT * 10))); do
+  if ! kill -0 "$pid" 2>/dev/null; then exited=1; break; fi
+  sleep 0.1
+done
+secs=$(( $(date +%s) - start ))
+steps="$(tr '\n' '|' < "$OUT" 2>/dev/null || true)"
+echo "smoke steps: $steps (after $secs s)"
+grep -E 'smoke:|close:|mpv: render' "$WORK/stdout.txt" | tail -20 || true
+if [[ $exited == 0 ]]; then kill -9 "$pid" 2>/dev/null || true; fi
+left="$(pgrep -f "$EXE" || true)"
+[[ -n "$left" ]] && kill -9 $left 2>/dev/null || true
+grep -qx start "$OUT" 2>/dev/null || { [[ $exited == 1 ]] && { echo "skipped: the app never came up"; exit 0; }; echo "did not come up nor exit" >&2; exit 1; }
+grep -q '^skip ' "$OUT" && { echo "skipped: $(grep '^skip ' "$OUT")"; exit 0; }
+grep -q '^fail ' "$OUT" && { echo "smoke failed: $(grep '^fail ' "$OUT")" >&2; exit 1; }
+grep -q '^opened ' "$OUT" || { echo "the media never opened" >&2; exit 1; }
+[[ $exited == 1 ]] || { echo "the app did not close within $LIMIT s (P32)" >&2; exit 1; }
+[[ -z "$left" ]] || { echo "a starsync process was left behind (P32)" >&2; exit 1; }
+echo "smoke ok: opened and closed in $secs s, no process left"