Rationalize optional dependencies vs dependency groups

Establish clear separation between user-facing optional dependencies
and developer-only dependency groups:

**Optional Dependencies (user features):**
- watcher: File watching service for batch processing
- webservice: Streamlit-based web UI
- Installable via: uv sync --extra <name> or pip install ocrmypdf[name]

**Dependency Groups (developer tools):**
- test: Testing infrastructure (merged from test + extended_test)
- docs: Documentation building tools
- streamlit-dev: Enhanced Streamlit development tools
- dev: General development tools (mypy, ipykernel)
- Installable via: uv sync --group <name> (uv only, NOT pip)

Breaking changes for developers:
- pip install -e .[test] no longer works → use uv sync --group test
- pip install -e .[docs] no longer works → use uv sync --group docs
- pip install -e .[extended_test] removed → merged into test group

No breaking changes for end users:
- pip install ocrmypdf[watcher] still works
- pip install ocrmypdf[webservice] still works

Updated:
- CI/CD workflows to use uv sync --group test
- Docker images to exclude test dependencies
- Documentation to recommend uv with pip as fallback
- pyproject.toml with clear comments explaining both systems

docs/batch.md

@@ -117,6 +117,10 @@ tend to give better performance. watcher.py works on all platforms.
 Users may need to customize the script to meet their requirements.
 
 :::{code} bash
+# Using uv (recommended)
+uv sync --extra watcher
+
+# Or using pip
 pip3 install ocrmypdf[watcher]
 
 env OCR_INPUT_DIRECTORY=/mnt/input-pdfs \