feat: 支持角色图片拖拽上传

[xyh202131]

Closes #765

改动说明

• Quick Start 支持将角色参考图拖入整块输入区域，并在拖拽时显示明确的释放提示。
• Workflow Editor 提供更大的图片拖入区域，同时保留点击选择文件的入口。
• 两处统一校验 PNG、JPG/JPEG、GIF、WEBP 格式与 10 MB 大小上限，并展示一致的错误提示。
• 复用现有上传、取消与 WorkflowRun 流程，不引入模拟接口或新的后端依赖。

验证

• npm test -- --exclude src/font-delivery.test.ts --maxWorkers=1：79 个测试文件、1209 项测试全部通过。
• Quick Start 与 Workflow Editor 定向测试：2 个测试文件、197 项测试全部通过。
• npm run lint：通过。
• npm run build：通过。
• 本次 6 个改动文件的 oxfmt --check：通过。

[vercel]

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Project	Deployment	Actions	Updated (UTC)
windup	Ready	Preview	Aug 26, 2026 9:20am

[codecov]

Codecov Report

❌ Patch coverage is 78.12500% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
frontend/src/shared/ui/image-drop-target.ts	75.55%	6 Missing and 5 partials ⚠️
frontend/src/pages/workflow-editor/index.tsx	81.81%	1 Missing and 1 partial ⚠️
frontend/src/pages/quick-start/index.tsx	87.50%	0 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #767      +/-   ##
==========================================
- Coverage   82.66%   82.62%   -0.05%     
==========================================
  Files         102      103       +1     
  Lines        9162     9220      +58     
  Branches     3034     3054      +20     
==========================================
+ Hits         7574     7618      +44     
- Misses        759      766       +7     
- Partials      829      836       +7     

Flag	Coverage Δ
frontend	82.62% <78.12%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
frontend/src/pages/quick-start/index.tsx	83.64% <87.50%> (-0.01%)	⬇️
frontend/src/pages/workflow-editor/index.tsx	83.52% <81.81%> (+0.03%)	⬆️
frontend/src/shared/ui/image-drop-target.ts	75.55% <75.55%> (ø)

... and 1 file with indirect coverage changes

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[huyanxius]

阻塞合并：lint-and-test 在 backend/packages/app/src/windup_app/server/orchestrator/executor.py:665 报 _LogProgress 未定义，请先修复 CI 后再合并。

[fennoai]

Reviewed the complete fixed diff against issue #765. The shared drop-target validates the accepted image MIME types and 10 MB limit before invoking either upload flow; both Quick Start and Workflow Editor wire picker and drag/drop paths, preserve disabled and cancellation behavior, and keep existing upload/session updates intact. git diff --check passes. Focused tests and typecheck were not executable in this workspace because the installed vitest and tsc commands return Permission denied.

No high-confidence correctness findings.