chore: add CI/CD pipeline for Gitea deployment

- Add .gitea/workflows/build.yml for tag-triggered builds
- Add Dockerfile for containerized deployment (port 8086)
- Add .dockerignore to keep image lean
- Add CHANGELOG.md following Keep a Changelog format
- Update AGENTS.md with deployment verification URL

Build pipeline:
1. Create Gitea release on v* tag
2. Build and push Docker image to git.schweitz.internal
3. Trigger Watchtower for automatic deployment

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

Dockerfile

@@ -0,0 +1,22 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Install system dependencies (curl for healthcheck)
+RUN apt-get update && apt-get install -y \
+    curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Python dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy application
+COPY pyproject.toml .
+COPY src/ ./src/
+
+ENV PYTHONPATH=/app
+
+EXPOSE 8086
+
+CMD ["uvicorn", "src.main:app", "--host", "0.0.0.0", "--port", "8086", "--workers", "1"]