fix: writing mode first-report allows only the pipeline to write the report

- Strip write_file/str_replace/bash from the model binding in the
  first-report run: after_model rewrites only fire after a full model
  response, so any bound write tool let weak models draft the whole
  essay into tool args (write_file content or bash cat>/python
  heredocs) for tens of invisible seconds before interception
- Hallucinated hand-writes are still handled: after_model rewrites
  bash cat >/python open('w')/tee and leftover write calls to
  deep_research_report; wrap_tool_call rejects whatever reaches the
  tool layer; post-success writes are dropped, nudged to a 2-3
  sentence summary, and patched with a fallback closing message so
  the turn never ends silently
- The rewritten pipeline call carries topic = original request
  (clarification answers skipped) plus focus = clarification answers,
  so the pipeline writes the clarified subject instead of the raw
  prompt text; prompts updated to match (tools unavailable, call the
  tool directly, do not draft first)
- Frontend write-step interception and streaming preview scoping now
  applies only in writing mode; normal mode shows/previews writes
  exactly as before

.gitignore

@@ -127,6 +127,9 @@ offline-backend-20260512/backend/tests/*
 !offline-backend-20260512/backend/tests/test_workflow_engine.py
 !offline-backend-20260512/backend/tests/test_workflow_runs.py
 !offline-backend-20260512/backend/tests/test_workflow_concurrency.py
+# Writing-mode first-report pipeline enforcement regressions.
+!offline-backend-20260512/backend/tests/test_writing_mode_report_middleware.py
+!offline-backend-20260512/backend/tests/test_writing_rewrite_prompt.py
 deploy
 .history