feat: Add Python fuzzing vertical with Atheris integration

This commit implements a complete Python fuzzing workflow using Atheris:

## Python Worker (workers/python/)
- Dockerfile with Python 3.11, Atheris, and build tools
- Generic worker.py for dynamic workflow discovery
- requirements.txt with temporalio, boto3, atheris dependencies
- Added to docker-compose.temporal.yaml with dedicated cache volume

## AtherisFuzzer Module (backend/toolbox/modules/fuzzer/)
- Reusable module extending BaseModule
- Auto-discovers fuzz targets (fuzz_*.py, *_fuzz.py, fuzz_target.py)
- Recursive search to find targets in nested directories
- Dynamically loads TestOneInput() function
- Configurable max_iterations and timeout
- Real-time stats callback support for live monitoring
- Returns findings as ModuleFinding objects

## Atheris Fuzzing Workflow (backend/toolbox/workflows/atheris_fuzzing/)
- Temporal workflow for orchestrating fuzzing
- Downloads user code from MinIO
- Executes AtherisFuzzer module
- Uploads results to MinIO
- Cleans up cache after execution
- metadata.yaml with vertical: python for routing

## Test Project (test_projects/python_fuzz_waterfall/)
- Demonstrates stateful waterfall vulnerability
- main.py with check_secret() that leaks progress
- fuzz_target.py with Atheris TestOneInput() harness
- Complete README with usage instructions

## Backend Fixes
- Fixed parameter merging in REST API endpoints (workflows.py)
- Changed workflow parameter passing from positional args to kwargs (manager.py)
- Default parameters now properly merged with user parameters

## Testing
✅ Worker discovered AtherisFuzzingWorkflow
✅ Workflow executed end-to-end successfully
✅ Fuzz target auto-discovered in nested directories
✅ Atheris ran 100,000 iterations
✅ Results uploaded and cache cleaned

workers/python/Dockerfile

@@ -0,0 +1,47 @@
+# FuzzForge Vertical Worker: Python Fuzzing
+#
+# Pre-installed tools for Python fuzzing and security analysis:
+# - Python 3.11
+# - Atheris (Python fuzzing)
+# - Common Python security tools
+# - Temporal worker
+
+FROM python:3.11-slim
+
+# Set working directory
+WORKDIR /app
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y \
+    # Build essentials for Atheris
+    build-essential \
+    clang \
+    llvm \
+    # Development tools
+    git \
+    curl \
+    wget \
+    # Cleanup
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Python dependencies for Temporal worker
+COPY requirements.txt /tmp/requirements.txt
+RUN pip3 install --no-cache-dir -r /tmp/requirements.txt && \
+    rm /tmp/requirements.txt
+
+# Create cache directory for downloaded targets
+RUN mkdir -p /cache && chmod 755 /cache
+
+# Copy worker entrypoint
+COPY worker.py /app/worker.py
+
+# Add toolbox to Python path (mounted at runtime)
+ENV PYTHONPATH="/app:/app/toolbox:${PYTHONPATH}"
+ENV PYTHONUNBUFFERED=1
+
+# Healthcheck
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD python3 -c "import sys; sys.exit(0)"
+
+# Run worker
+CMD ["python3", "/app/worker.py"]