feat: 视频缩略图生成、最近文件面板与前端视图重构

- 新增 VideoThumbnailService，基于 ffmpeg 截取视频缩略图，ffprobe 提取时长
  - 新增 ManagedThumbnailMap 模型及多数据库迁移，存储缩略图元数据
  - 新增 /api/thumbnails/{id} 缩略图流端点
  - 新增最近添加/最近播放 API 与前端面板，支持列表/网格双视图切换
  - FileRecordDto 扩展 thumbnailUrl、videoDuration、lastPlayedAt 字段
  - 前端新增文件库 Tab 导航、卡片网格视图、视频海报与时长信息栏
  - 添加文件库目录不再同步全量扫描，改为后台异步自动扫描

FileShare-EFCore/Migrations/SQLite/SqliteAppDataContextModelSnapshot.cs

@@ -1,4 +1,4 @@
-// <auto-generated />
+// <auto-generated />
 using System;
 using FileShare_EFCore.Database;
 using Microsoft.EntityFrameworkCore;
@@ -116,6 +116,10 @@ namespace FileShare_EFCore.Migrations.SQLite
                         .HasColumnType("TEXT")
                         .HasColumnName("file-name");
 
+                    b.Property<DateTime?>("LastPlayedAt")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("last-played-at");
+
                     b.Property<DateTime>("LastSeenAt")
                         .HasColumnType("TEXT")
                         .HasColumnName("last-seen-at");
@@ -144,10 +148,18 @@ namespace FileShare_EFCore.Migrations.SQLite
                         .HasColumnType("INTEGER")
                         .HasColumnName("size-bytes");
 
+                    b.Property<int?>("ThumbnailId")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("thumbnail-id");
+
                     b.Property<DateTime>("UpdatedAt")
                         .HasColumnType("TEXT")
                         .HasColumnName("updated-at");
 
+                    b.Property<double?>("VideoDuration")
+                        .HasColumnType("REAL")
+                        .HasColumnName("video-duration");
+
                     b.HasKey("Id")
                         .HasName("pk-managed-file-record");
 
@@ -155,9 +167,15 @@ namespace FileShare_EFCore.Migrations.SQLite
                         .IsUnique()
                         .HasDatabaseName("idx-managed-file-record-absolute-path");
 
+                    b.HasIndex("LastPlayedAt")
+                        .HasDatabaseName("idx-managed-file-record-last-played-at");
+
                     b.HasIndex("LibraryRootId")
                         .HasDatabaseName("idx-managed-file-record-root-id");
 
+                    b.HasIndex("ThumbnailId")
+                        .HasDatabaseName("idx-managed-file-record-thumbnail-id");
+
                     b.HasIndex("MediaType", "Exists")
                         .HasDatabaseName("idx-managed-file-record-media-type-exists");
 
@@ -234,6 +252,53 @@ namespace FileShare_EFCore.Migrations.SQLite
                         });
                 });
 
+            modelBuilder.Entity("FileShare_EFCore.Models.ManagedThumbnailMap", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("id");
+
+                    b.Property<string>("ContentType")
+                        .IsRequired()
+                        .HasMaxLength(100)
+                        .HasColumnType("TEXT")
+                        .HasColumnName("content-type");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("created-at");
+
+                    b.Property<int>("LibraryRootId")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("library-root-id");
+
+                    b.Property<string>("RelativePath")
+                        .IsRequired()
+                        .HasMaxLength(1024)
+                        .HasColumnType("TEXT")
+                        .HasColumnName("relative-path");
+
+                    b.Property<DateTime>("UpdatedAt")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("updated-at");
+
+                    b.HasKey("Id")
+                        .HasName("pk-managed-thumbnail-map");
+
+                    b.HasIndex("LibraryRootId")
+                        .HasDatabaseName("idx-managed-thumbnail-map-root-id");
+
+                    b.HasIndex("RelativePath")
+                        .IsUnique()
+                        .HasDatabaseName("idx-managed-thumbnail-map-relative-path");
+
+                    b.ToTable("managed-thumbnail-map", t =>
+                        {
+                            t.HasComment("文件缩略图映射记录");
+                        });
+                });
+
             modelBuilder.Entity("FileShare_EFCore.Models.UserEntity", b =>
                 {
                     b.Property<int>("Id")
@@ -336,10 +401,35 @@ namespace FileShare_EFCore.Migrations.SQLite
                         .OnDelete(DeleteBehavior.Cascade)
                         .IsRequired();
 
+                    b.HasOne("FileShare_EFCore.Models.ManagedThumbnailMap", "Thumbnail")
+                        .WithMany("Files")
+                        .HasForeignKey("ThumbnailId")
+                        .OnDelete(DeleteBehavior.SetNull);
+
+                    b.Navigation("LibraryRoot");
+
+                    b.Navigation("Thumbnail");
+                });
+
+            modelBuilder.Entity("FileShare_EFCore.Models.ManagedThumbnailMap", b =>
+                {
+                    b.HasOne("FileShare_EFCore.Models.ManagedLibraryRoot", "LibraryRoot")
+                        .WithMany("Thumbnails")
+                        .HasForeignKey("LibraryRootId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
                     b.Navigation("LibraryRoot");
                 });
 
             modelBuilder.Entity("FileShare_EFCore.Models.ManagedLibraryRoot", b =>
+                {
+                    b.Navigation("Files");
+
+                    b.Navigation("Thumbnails");
+                });
+
+            modelBuilder.Entity("FileShare_EFCore.Models.ManagedThumbnailMap", b =>
                 {
                     b.Navigation("Files");
                 });