M1: backend core + proposal engine

- FastAPI skeleton, SQLAlchemy models (§13), Alembic initial migration
- SchedulingProvider interface with google_calendar (free/busy read-only),
  partner_api (Appendix B client) and mock implementations
- Proposal engine: create → provider-routed delivery → owner actions
  (resolve/confirm+SMS/reject) → expiry + reminders (§9)
- Signed single-use action links, .ics METHOD:REQUEST attachment
- Partner outcome webhook with HMAC verification + polling fallback
- SmsProvider (console) with Bosnian templates (§5.5), EmailProvider (console/SMTP)
- Fake partner API server in tests/ — Appendix B reference implementation
- 43 tests: slot math, proposal lifecycle, action links, partner contract

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,12 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+COPY pyproject.toml README.md* ./
+COPY gogo ./gogo
+COPY alembic ./alembic
+COPY alembic.ini ./
+
+RUN pip install --no-cache-dir -e .
+
+EXPOSE 8000
+CMD ["uvicorn", "gogo.main:app", "--host", "0.0.0.0", "--port", "8000"]