feat: Transform to web architecture with FastAPI backend

This major update transforms leggen from CLI-only to a web-ready
architecture while maintaining full CLI compatibility.

New Features:
- FastAPI backend service (leggend) with comprehensive REST API
- Background job scheduler with configurable cron (replaces Ofelia)
- All CLI commands refactored to use API endpoints
- Docker configuration updated for new services
- API client with health checks and error handling

API Endpoints:
- /api/v1/banks/* - Bank connections and institutions
- /api/v1/accounts/* - Account management and balances
- /api/v1/transactions/* - Transaction retrieval with filtering
- /api/v1/sync/* - Manual sync and scheduler configuration
- /api/v1/notifications/* - Notification settings management

CLI Enhancements:
- New --api-url option and LEGGEND_API_URL environment variable
- Enhanced sync command with --wait and --force options
- Improved transactions command with --full and --limit options
- Automatic fallback and health checking

Breaking Changes:
- compose.yml structure updated (leggend service added)
- Ofelia scheduler removed (internal scheduler used instead)

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

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

Dockerfile.leggend

@@ -0,0 +1,32 @@
+FROM python:3.13-alpine AS builder
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /bin/
+
+WORKDIR /app
+
+RUN --mount=type=cache,target=/root/.cache/uv \
+    --mount=type=bind,source=uv.lock,target=uv.lock \
+    --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
+    uv sync --frozen --no-install-project --no-editable
+
+COPY . /app
+
+RUN --mount=type=cache,target=/root/.cache/uv \
+    uv sync --frozen --no-editable --no-group dev
+
+FROM python:3.13-alpine
+
+LABEL org.opencontainers.image.source="https://github.com/elisiariocouto/leggen"
+LABEL org.opencontainers.image.authors="Elisiário Couto <elisiario@couto.io>"
+LABEL org.opencontainers.image.licenses="MIT"
+LABEL org.opencontainers.image.title="leggend"
+LABEL org.opencontainers.image.description="Leggen API service"
+LABEL org.opencontainers.image.url="https://github.com/elisiariocouto/leggen"
+
+WORKDIR /app
+ENV PATH="/app/.venv/bin:$PATH"
+
+COPY --from=builder --chown=app:app /app/.venv /app/.venv
+
+EXPOSE 8000
+
+ENTRYPOINT ["/app/.venv/bin/leggend"]