fix(web): improve deferred generated-file download controls

[techotaku39]

Summary

• Fix the deferred generated-file download control by replacing the oversized placeholder with a compact action.
• Add a metadata-only generated-file request so the UI can show the file size without downloading the file contents.
• Localize deferred media actions and display the file size in both the prepare and final download states while preserving the original filename.
• Add regression coverage across the CLI handler, Hub route, shared API type, Web component, and live download flow.

Validation

• bun typecheck — passed.
• pwsh -NoProfile -File .\scripts\Invoke-HapiTaskPlaywright.ps1 -Name web-media-download-ux -Suite Root -TestArgs terminal-wrap-fidelity.spec.ts — 2 passed.
• Web generated-media tests — 10 passed.
• Hub generated-image route tests — 10 passed.
• CLI file-handler tests — 2 passed.
• Shared package tests — 294 passed.
• bun run build — passed.
• git diff --check — passed.
• Live Playwright download flow — 1 passed:
  • Verified 加载文件（20 KB）.
  • Verified 下载文件（20 KB）.
  • Verified the downloaded filename remains Cursor Plan A Markdown 导出.zip.
• Local and public health checks — HTTP 200.

Related Issues

None

AI Disclosure

Implemented and validated with OpenAI Codex (GPT-5.6).