feat: UOOC/Zhihuishu dual-platform brushing platform

- ASP.NET Core 9 Web API backend with JWT auth, EF Core MySQL
- Vue 3 + Vite + Pinia + Ant Design Vue frontend
- Multi-platform connection management (UOOC & Zhihuishu)
- Video brushing with AES-CBC encryption for Zhihuishu
- Multi-task queue with cross-platform parallel execution
- Task persistence via MySQL database
- Progress tracking with inline catalog enrichment
- Mobile-responsive UI

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/src/UoocProgress.Api/Controllers/PlatformChallengesController.cs

@@ -0,0 +1,37 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using UoocProgress.Api.Models;
+using UoocProgress.Api.Services;
+
+namespace UoocProgress.Api.Controllers;
+
+[ApiController]
+[Authorize(Policy = "UserOrAdmin")]
+[Route("api/platform-challenges")]
+public sealed class PlatformChallengesController(ChallengeSessionService challengeSessionService) : ControllerBase
+{
+    [HttpGet("{challengeSessionId}")]
+    [ProducesResponseType<ChallengeSessionDto>(StatusCodes.Status200OK)]
+    [ProducesResponseType<ProblemDetails>(StatusCodes.Status404NotFound)]
+    public ActionResult<ChallengeSessionDto> GetChallenge(string challengeSessionId)
+    {
+        var claimValue = User.FindFirstValue(ClaimTypes.NameIdentifier);
+        var userId = long.TryParse(claimValue, out var parsed)
+            ? parsed
+            : throw new InvalidOperationException("当前登录态无效。");
+
+        var challenge = challengeSessionService.Get(challengeSessionId, userId);
+        if (challenge is null)
+        {
+            return NotFound(new ProblemDetails
+            {
+                Title = "挑战会话不存在",
+                Detail = "未找到对应的挑战会话。",
+                Status = StatusCodes.Status404NotFound
+            });
+        }
+
+        return Ok(challenge);
+    }
+}