feat(converter): implement deterministic JSON to Markdown article converter (spec 005)

specs/005-convert-json-markdown/quickstart.md

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+# Quickstart: Convert Article JSON to Markdown
+
+**Feature**: `005-convert-json-markdown` | **Date**: 2026-08-21
+
+## 1. Prerequisites & Setup
+
+Ensure the environment has dependencies installed:
+
+```bash
+pip install -r requirements.txt
+```
+
+Verify that `markdownify` is installed:
+
+```bash
+python -c "import markdownify; print(markdownify.__version__)"
+```
+
+---
+
+## 2. Running the CLI Tool
+
+### Basic Conversion (Default Output Path)
+
+Convert a single article JSON to `<stem>.md` in the same directory:
+
+```bash
+python scripts/convert_article_to_markdown.py -i out/river_plate_extracted_selected_001.json
+```
+
+Output generated: `out/river_plate_extracted_selected_001.md`.
+
+### Custom Destination Path
+
+Specify an explicit output path:
+
+```bash
+python scripts/convert_article_to_markdown.py \
+  -i out/river_plate_extracted_selected_001.json \
+  -o out/markdown/river_plate_article_001.md
+```
+
+---
+
+## 3. Verification & Testing
+
+### Run All Unit & Integration Tests
+
+```bash
+pytest tests/test_convert_article_to_markdown.py -v
+```
+
+### Run Linter & Type Checker
+
+```bash
+ruff check scripts/convert_article_to_markdown.py src/ tests/
+mypy scripts/convert_article_to_markdown.py
+```