feat(playback): client direct-play decode mode (release host transcoding)

Add an admin toggle playback.direct_only that offloads all decoding to the
client. When enabled:
- Emby PlaybackInfo no longer advertises SupportsTranscoding nor a
  TranscodingUrl, forcing Emby/Infuse/Yamby clients to direct play.
- HLS endpoints refuse (ErrTranscodeDisabled) so the host never spawns ffmpeg.
- Web player forces direct play, hides the HLS toggle, and surfaces a hint.
Exposed via /system/info (direct_play_only) and the Settings page.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

web/src/api/system.ts

@@ -13,6 +13,7 @@ export const systemAPI = {
         arch: string
         data_dir: string
         cache_dir: string
+        direct_play_only?: boolean
       }>('/system/info')
       .then((r) => r.data),
 

web/src/pages/PlayerPage.tsx

@@ -8,6 +8,7 @@ import { mediaAPI } from '../api/library'
 import { api, hlsURL, streamURL } from '../api/client'
 import { playbackAPI } from '../api/playback'
 import { subtitlesAPI, type SubtitleTrack } from '../api/subtitles'
+import { systemAPI } from '../api/system'
 import type { Media } from '../types'
 
 type Mode = 'direct' | 'hls'
@@ -37,6 +38,16 @@ export function PlayerPage() {
   const [subs, setSubs] = useState<SubtitleTrack[]>([])
   const [hlsUnavailable, setHlsUnavailable] = useState(false)
   const [playerError, setPlayerError] = useState('')
+  // 「客户端直连解码」模式：宿主机不转码，播放器强制 direct play、隐藏 HLS 切换。
+  const [directOnly, setDirectOnly] = useState(false)
+
+  // 读取宿主机的「直连解码」开关。开启时全程 direct play，不走 HLS。
+  useEffect(() => {
+    systemAPI
+      .info()
+      .then((info) => setDirectOnly(Boolean(info.direct_play_only)))
+      .catch(() => setDirectOnly(false))
+  }, [])
 
   // Load metadata and pick a default mode.
   useEffect(() => {
@@ -45,14 +56,15 @@ export function PlayerPage() {
       setMedia(m)
       const forced = params.get('mode') as Mode | null
       const auto = pickMode(m)
-      setMode(forced ?? auto)
+      // 直连解码模式下忽略 ?mode=hls 与自动判定，始终 direct play。
+      setMode(directOnly ? 'direct' : (forced ?? auto))
       setPlayerError('')
     })
     subtitlesAPI
       .list(id)
       .then((tracks) => setSubs(tracks ?? []))
       .catch(() => setSubs([]))
-  }, [id, params])
+  }, [id, params, directOnly])
 
   // Wire up the actual <video> element when we know the mode.
   useEffect(() => {
@@ -161,26 +173,35 @@ export function PlayerPage() {
           <ArrowLeft size={16} /> 返回
         </button>
 
-        <button
-          onClick={() => {
-            const next = mode === 'hls' ? 'direct' : 'hls'
-            setMode(next)
-            params.set('mode', next)
-            setParams(params, { replace: true })
-          }}
-          className="pointer-events-auto flex items-center gap-2 rounded-full border border-white/15 bg-black/70 px-4 py-2 text-sm font-medium text-white shadow-xl backdrop-blur transition hover:bg-black/85"
-          title="切换播放模式"
-        >
-          {mode === 'hls' ? (
-            <>
-              <RefreshCw size={14} /> HLS 转码中
-            </>
-          ) : (
-            <>
-              <Sparkles size={14} /> 直接播放
-            </>
-          )}
-        </button>
+        {directOnly ? (
+          <span
+            className="pointer-events-auto flex items-center gap-2 rounded-full border border-white/15 bg-black/70 px-4 py-2 text-sm font-medium text-white shadow-xl backdrop-blur"
+            title="宿主机不转码，由客户端本地解码直连"
+          >
+            <Sparkles size={14} /> 客户端直连解码
+          </span>
+        ) : (
+          <button
+            onClick={() => {
+              const next = mode === 'hls' ? 'direct' : 'hls'
+              setMode(next)
+              params.set('mode', next)
+              setParams(params, { replace: true })
+            }}
+            className="pointer-events-auto flex items-center gap-2 rounded-full border border-white/15 bg-black/70 px-4 py-2 text-sm font-medium text-white shadow-xl backdrop-blur transition hover:bg-black/85"
+            title="切换播放模式"
+          >
+            {mode === 'hls' ? (
+              <>
+                <RefreshCw size={14} /> HLS 转码中
+              </>
+            ) : (
+              <>
+                <Sparkles size={14} /> 直接播放
+              </>
+            )}
+          </button>
+        )}
       </div>
 
       <div className="flex flex-1 items-center justify-center">
@@ -195,7 +216,10 @@ export function PlayerPage() {
               // 浏览器对 <video src> 的错误描述非常有限，把详细原因
               // 转给开发者控制台 + 一条 toast；常见原因是 codec 不支持。
               if (mode === 'direct') {
-                if (hlsUnavailable) {
+                if (directOnly) {
+                  setPlayerError('直接播放失败。当前为「客户端直连解码」模式，宿主机不转码；请使用支持该编码/封装的播放器（如 Infuse / VLC / Emby 客户端）播放，或关闭直连解码模式。')
+                  toast.error('直接播放失败（客户端直连解码模式）')
+                } else if (hlsUnavailable) {
                   setPlayerError('直接播放失败，且 HLS 转码不可用。请检查文件是否存在，或配置本机 ffmpeg 后使用 HLS 转码播放。')
                   toast.error('直接播放失败，HLS 转码不可用')
                 } else {

web/src/pages/SettingsPage.tsx

@@ -47,11 +47,18 @@ const GROUPS: SettingGroup[] = [
           { value: 'ja-JP', label: '日本語' },
         ],
       },
+      {
+        key: 'playback.direct_only',
+        label: '客户端直连解码（释放宿主机资源）',
+        type: 'toggle',
+        hint: '默认关闭。开启后宿主机不再进行任何 FFmpeg 转码，所有播放交给第三方客户端（Infuse / VLC / Emby 客户端等）或浏览器本地解码直连（direct play / 302 直链），大幅降低宿主机 CPU 占用。若客户端不支持源编码可能无法播放。',
+        defaultValue: 'false',
+      },
       {
         key: 'transcode.enabled',
         label: '启用转码',
         type: 'toggle',
-        hint: '关闭后所有视频直连播放',
+        hint: '关闭后所有视频直连播放（「客户端直连解码」开启时本项自动失效）',
         defaultValue: 'true',
       },
       {