feat(agent-compose): upload Dify files to agent workspaces

[kingfs]

Summary

• add optional files and workspace_id inputs to both agent-compose workflow and strategy plugins
• upload Dify SDK File contents to request-isolated agent-compose workspace paths
• include uploaded workspace paths in the agent prompt
• enforce sanitized filenames and 50 MiB per-file / 100 MiB per-request limits
• document the workspace upload configuration in English and Chinese

User impact

Dify users can attach documents to either integration and make those files available inside the selected agent workspace. Existing file-free workflows remain backward compatible. Because the current agent-compose project response does not provide a reliable agent-to-workspace ID mapping, users should explicitly configure workspace_id when files are supplied.

Testing

• task check for agent_compose_workflow (28 passed, 83.67% coverage)
• task check for agent_compose_strategy (32 passed, 84.81% coverage)
• task build (validation and tests pass; final packaging could not run because the local dify plugin CLI is not installed)
• Documentation and changelog updated where applicable
• No secrets, internal addresses, private dependencies, or generated packages