[Pollo3470]

Summary

• expose an authenticated remote MCP host backed by the shared typed tool runtime
• add project-scoped remote planning, maintenance, content readers, text generation, script patching, draft workflows, and project entry tools
• keep embedded tools bound to the current session project while remote tools require an explicit project
• provide progress heartbeats for synchronous remote text generation

Scope

• upload_source accepts UTF-8 text sources with .txt or .md filenames in this stage; DOCX, EPUB, and PDF transport are not included
• draft promotion and discard use revision-based optimistic concurrency control
• deployment documentation contains host configuration only; individual tool contracts remain in MCP schemas

Validation

• backend: 10,391 passed, 2 skipped
• frontend: 156 files, 1,898 tests passed
• website checks passed
• Ruff, formatting, basedpyright, import contracts, and test audit passed
• independent Stage 2 scope/spec audit completed; remediation is included in the current HEAD
• AI reviewer and required-check convergence is pending for the current HEAD

Closes #2067
Closes #2068
Closes #2069
Closes #2070
Closes #2072
Closes #2073
Closes #2074

Refs #2062

Summary by CodeRabbit

• 新功能

  • 支持通过远程 MCP 管理项目、源文件、剧本、草稿和项目文件。
  • 新增项目创建、列表、源文件上传及 Step 1 内容生成。
  • 草稿支持打开、修改、晋升和丢弃，覆盖多种内容类型。

• 改进

  • 剧本编辑支持批量更新、插入、删除和拆分，并增加版本冲突校验。
  • 优化结构化错误响应、并发处理、资产清理及多语言界面文案。
  • 旁白分段标识校验更加严格。

• 安全性

  • 加强路径、符号链接、文件锁及迁移失败保护。
  • 远程 MCP 支持 API 密钥认证、主机和来源白名单、CORS 配置及请求体大小限制。