feat: hwaccel + Fanart/TheTVDB + AI + Discover + NFO + Tasks + Recycle bin

Backend
  - service/transcoder.go: encoder selector (software / nvenc / qsv /
    vaapi) with proper hwaccel + scale_* filters per encoder; configurable
    bitrate/preset/height/segment-seconds via transcoder.* config; new
    Active() snapshot + ActiveJob struct for the Tasks panel; unit-tested
    via buildFFmpegArgs(...).
  - service/thetvdb.go: TheTVDB v4 provider — login() caches the JWT for
    24h, SearchSeries() returns Match struct.
  - service/fanart.go: Fanart.tv provider — high-res movie artwork keyed
    by TMDb id; used to upgrade poster/backdrop after a successful match.
  - service/scraper.go: provider chain reworked — anime → Bangumi, tv →
    TheTVDB, default → TMDb, with optional Fanart upgrade post-match.
  - service/discover.go: TMDb /trending/movie/day + /movie/popular for
    the Discover rail.
  - service/ai.go: OpenAI-compatible client. SmartSearch() turns a free-
    form query into a structured SearchIntent JSON; Recommend() emits a
    short list of titles given the user's history. Disabled when
    ai.api_key is empty.
  - service/nfo.go: per-movie .nfo writer (Kodi/Jellyfin schema) +
    library-scope batch exporter.
  - service/media.go: SoftDelete / Restore / Purge / ListRecycleBin
    helpers backed by gorm Unscoped().
  - service/service.go: container wires Fanart, TheTVDB, Discover, AI,
    NFO; everything still tears down cleanly via Close().
  - config: new transcoder.* section (encoder, preset, video_bitrate,
    max_rate, buf_size, max_height, segment_seconds) with sensible
    defaults.

Handlers / routes
  - new files: discover.go, recycle.go, nfo.go, ai.go, tasks.go.
  - registers GET /tasks, /discover/{trending,popular},
    /ai/{status,search,recommend}; admin-only GET /recycle and
    DELETE/POST /media/:id (soft delete / restore / purge); admin-only
    POST /media/:id/nfo and /libraries/:id/nfo.

Frontend
  - new pages: DiscoverPage, TasksPage, RecycleBinPage; SearchPage gains
    an optional AI smart-search toggle that calls /api/ai/search.
  - MediaDetailPage gains admin actions for 导出 NFO and 移至回收站.
  - new api/ helpers: ai.ts, discover.ts, recycle.ts, tasks.ts.
  - App.tsx routes /discover, /tasks, /recycle (last two admin-only).
  - Layout sidebar groups now include Discover + Tasks + Recycle Bin.

Docker / config
  - Dockerfile: adds intel-media-driver / libva-utils / mesa-va-gallium
    so QSV + VAAPI work out of the box on Intel iGPUs.
  - docker-compose.yml: documents devices + group_add + nvidia runtime
    overrides for hardware transcoding.

Verified: go build, go vet, go test (incl. new TestBuildFFmpegArgs across
software / nvenc / qsv / vaapi encoder profiles); tsc -b && vite build
emits 22 route chunks plus the deferred hls chunk; main bundle 248 KB /
83 KB gzipped.

internal/config/config.go

@@ -30,13 +30,25 @@ const EnvPrefix = "MEDIASTATION"
 
 // Config is the root config aggregate.
 type Config struct {
-	App      AppConfig      `mapstructure:"app"`
-	Database DatabaseConfig `mapstructure:"database"`
-	Secrets  SecretsConfig  `mapstructure:"secrets"`
-	Logging  LoggingConfig  `mapstructure:"logging"`
-	Cache    CacheConfig    `mapstructure:"cache"`
-	Media    MediaConfig    `mapstructure:"media"`
-	AI       AIConfig       `mapstructure:"ai"`
+	App        AppConfig        `mapstructure:"app"`
+	Database   DatabaseConfig   `mapstructure:"database"`
+	Secrets    SecretsConfig    `mapstructure:"secrets"`
+	Logging    LoggingConfig    `mapstructure:"logging"`
+	Cache      CacheConfig      `mapstructure:"cache"`
+	Media      MediaConfig      `mapstructure:"media"`
+	Transcoder TranscoderConfig `mapstructure:"transcoder"`
+	AI         AIConfig         `mapstructure:"ai"`
+}
+
+// TranscoderConfig controls the HLS / ffmpeg backend.
+type TranscoderConfig struct {
+	Encoder        string `mapstructure:"encoder"` // "" / nvenc / qsv / vaapi
+	Preset         string `mapstructure:"preset"`
+	VideoBitrate   string `mapstructure:"video_bitrate"`
+	MaxRate        string `mapstructure:"max_rate"`
+	BufSize        string `mapstructure:"buf_size"`
+	MaxHeight      int    `mapstructure:"max_height"`
+	SegmentSeconds int    `mapstructure:"segment_seconds"`
 }
 
 // AppConfig holds runtime app parameters.
@@ -195,6 +207,14 @@ func setDefaults(v *viper.Viper) {
 	v.SetDefault("ai.model", "gpt-4o-mini")
 	v.SetDefault("ai.timeout", 30)
 	v.SetDefault("ai.max_concurrent", 3)
+
+	v.SetDefault("transcoder.encoder", "")
+	v.SetDefault("transcoder.preset", "veryfast")
+	v.SetDefault("transcoder.video_bitrate", "1500k")
+	v.SetDefault("transcoder.max_rate", "1800k")
+	v.SetDefault("transcoder.buf_size", "3000k")
+	v.SetDefault("transcoder.max_height", 720)
+	v.SetDefault("transcoder.segment_seconds", 4)
 }
 
 // normalize fills derived defaults and self-heals empty critical fields.