Phase 5: Timefold timetable-solver-service + solution persistence

school-service additions:
  - tt_solution + tt_lesson migration. tt_lesson carries three UNIQUEs
    (solution+class, solution+teacher, solution+room per slot) so the
    DB itself rejects any double-booking the solver might emit by
    mistake.
  - Solution CRUD + GET solutions/:id/lessons endpoint with joined
    class/subject/teacher/room names for display.
  - POST /timetable/solutions creates the row then fires off the
    solver-service via HTTP (5s timeout, mark failed if unreachable).
  - SOLVER_SERVICE_URL config wired through main.go/handlers.

New service timetable-solver-service:
  - Python 3.11 + FastAPI + Timefold Solver 1.21 (Apache-2.0). Dockerfile
    bundles OpenJDK 17 since Timefold for Python is a JPype bridge.
  - app/domain.py — Timefold @planning_entity Lesson with timeslot+room
    as PlanningVariables; @planning_solution Timetable holds problem
    facts (rooms/teachers/etc.) AND rule-fact collections.
  - app/rules.py — frozen dataclasses mirroring 6 of the 15 tt_
    constraint_* tables initially.
  - app/constraints.py — ConstraintProvider with 3 universal hard
    constraints (no double-booking) + 5 DB-driven constraints
    (teacher_unavailable_day/window, teacher_excluded_room,
    room_unavailable, room_requires_type) + 1 quality soft constraint
    (subject_preferred_period). Remaining 9 constraint types ready to
    plug in via the same join pattern.
  - app/repository.py — async loaders for stammdaten + rules; builds
    one Lesson per (curriculum row × weekly_hours), skipping rows
    without a tt_assignment teacher.
  - app/runner.py — runs solver in ThreadPoolExecutor so the FastAPI
    event loop stays responsive. Updates tt_solution status
    pending→running→completed|infeasible|failed.
  - app/main.py — POST /api/v1/solve (202 Accepted, background task),
    GET /api/v1/jobs/{id}, /health. School-service polls tt_solution
    directly instead of GET /jobs for the typical case.
  - docker-compose.yml adds the service on port 8095, depending on
    core-health-check.

Tests:
  - school-service: validator test for CreateTimetableSolutionRequest
    (allows empty name).
  - solver-service: tests/test_domain.py + tests/test_rules.py cover
    construction + hashability of the planning facts. Full solve flow
    deferred to Phase 8 integration with seed data.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

timetable-solver-service/Dockerfile

@@ -0,0 +1,30 @@
+# Timetable solver — Timefold needs a JVM at runtime, so this image bundles
+# OpenJDK 17 alongside Python 3.11.
+FROM eclipse-temurin:17-jdk-alpine AS jdk
+
+FROM python:3.11-slim
+
+# Pull the JVM from the temurin image so we don't shell out to apt for a JDK
+# (which on slim adds ~400 MB).
+COPY --from=jdk /opt/java/openjdk /opt/java/openjdk
+ENV JAVA_HOME=/opt/java/openjdk
+ENV PATH="${JAVA_HOME}/bin:${PATH}"
+
+WORKDIR /app
+
+# Install runtime deps the JVM bridge needs.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        libgomp1 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY app ./app
+
+EXPOSE 8095
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=30s --retries=3 \
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8095/health')" || exit 1
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8095"]