fix(file): save uploads to conversation workspace

[xiaolaili]

Problem

File uploads currently ignore the save_upload_to_workspace setting.

When system_settings.save_upload_to_workspace is enabled, files uploaded from a conversation should be saved into that conversation's workspace directory. Instead, the upload service always writes to the process temp directory under aionui/<conversation_id>.

Example from a container deployment:

• Expected: /data/conversations/claude-temp-a119bb34/<file>
• Actual: /data/config/temp/aionui/a119bb34/<file>

This makes uploaded files unavailable from the active conversation workspace even though the UI setting says uploads should be saved there.

Root Cause

The file upload path in aionui-file only uses std::env::temp_dir().join("aionui"). After the v2 migration to AionCore, the upload service does not resolve:

• system_settings.save_upload_to_workspace
• the current conversation by conversation_id
• the workspace path stored in conversation.extra.workspace

Changes

• Inject settings and conversation repositories into FileService.
• Honor system_settings.save_upload_to_workspace for /api/fs/upload.
• When enabled and a valid conversation_id is provided, resolve the conversation workspace from conversation.extra.workspace and save uploads there.
• Preserve existing temp-directory fallback behavior when:
  • no conversation_id is provided
  • the setting is disabled or missing
  • the conversation cannot be found
  • the conversation has no valid workspace metadata
• Add unit and E2E coverage for workspace upload behavior.

Testing

• cargo fmt --all -- --check
• cargo test -p aionui-file
• cargo test -p aionui-app --test file_e2e
• cargo clippy -p aionui-file -p aionui-app -- -D warnings