Remove Docker support files and documentation

Remove Docker deployment files and all references from README:
- Deleted Dockerfile
- Deleted docker-compose.yml (production)
- Deleted docker-compose.dev.yml (development)
- Removed Docker from Tech Stack section
- Removed Docker Deployment section from README

Docker support may be revisited and added back in the future.
For now, focus is on manual deployment as documented in the
Production Setup Guide.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Dockerfile

@@ -1,36 +0,0 @@
-# KeepItGoing Server Dockerfile
-FROM python:3.12-slim
-
-# Set environment variables
-ENV PYTHONDONTWRITEBYTECODE=1
-ENV PYTHONUNBUFFERED=1
-
-# Set work directory
-WORKDIR /app
-
-# Install system dependencies
-RUN apt-get update && apt-get install -y \
-    libpq-dev \
-    gcc \
-    && rm -rf /var/lib/apt/lists/*
-
-# Install Python dependencies
-COPY requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
-
-# Copy project
-COPY . .
-
-# Collect static files
-RUN python manage.py collectstatic --noinput --settings=config.settings.selfhosted || true
-
-# Create non-root user
-RUN addgroup --system appgroup && adduser --system --group appuser
-RUN chown -R appuser:appgroup /app
-USER appuser
-
-# Expose port
-EXPOSE 8000
-
-# Run gunicorn
-CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "4", "config.wsgi:application"]