fix: rename present_file to present_files in docs and prompts (#2393)

The tool is registered as `present_files` (plural) in present_file_tool.py,
but four references in documentation and prompt strings incorrectly used the
singular form `present_file`. This could cause confusion and potentially
lead to incorrect tool invocations.

Changed files:
- backend/docs/GUARDRAILS.md
- backend/docs/ARCHITECTURE.md
- backend/packages/harness/deerflow/agents/lead_agent/prompt.py (2 occurrences)

backend/packages/harness/deerflow/agents/lead_agent/prompt.py

@@ -420,7 +420,7 @@ You: "Deploying to staging..." [proceed]
 - Treat `/mnt/user-data/workspace` as your default current working directory for coding and file-editing tasks
 - When writing scripts or commands that create/read files from the workspace, prefer relative paths such as `hello.txt`, `../uploads/data.csv`, and `../outputs/report.md`
 - Avoid hardcoding `/mnt/user-data/...` inside generated scripts when a relative path from the workspace is enough
-- Final deliverables must be copied to `/mnt/user-data/outputs` and presented using `present_file` tool
+- Final deliverables must be copied to `/mnt/user-data/outputs` and presented using `present_files` tool
 {acp_section}
 </working_directory>
 
@@ -648,7 +648,7 @@ def _build_acp_section() -> str:
         "- ACP agents (e.g. codex, claude_code) run in their own independent workspace — NOT in `/mnt/user-data/`\n"
         "- When writing prompts for ACP agents, describe the task only — do NOT reference `/mnt/user-data` paths\n"
         "- ACP agent results are accessible at `/mnt/acp-workspace/` (read-only) — use `ls`, `read_file`, or `bash cp` to retrieve output files\n"
-        "- To deliver ACP output to the user: copy from `/mnt/acp-workspace/<file>` to `/mnt/user-data/outputs/<file>`, then use `present_file`"
+        "- To deliver ACP output to the user: copy from `/mnt/acp-workspace/<file>` to `/mnt/user-data/outputs/<file>`, then use `present_files`"
     )