Phase 7: pinning, plan versions, solver budget + UX polish

Backend (school-service):
  - tt_solution gains parent_solution_id (self-FK, ON DELETE SET NULL)
    and seconds_limit columns via ALTER TABLE IF NOT EXISTS.
  - CreateTimetableSolutionRequest accepts optional parent_solution_id
    and seconds_limit (5-600s) with binding validation.
  - CreateSolution checks parent ownership before INSERT so users can't
    fork another tenant's plan.
  - New PUT /timetable/lessons/:id/pin endpoint; ownership enforced via
    the lesson's solution.created_by_user_id JOIN.

Solver:
  - Lesson.pinned now carries @PlanningPin so Timefold leaves locked
    cells untouched during the search.
  - build_problem() takes optional parent_solution_id; if set, copies
    pinned (class_id, subject_id, day, period, room) tuples onto fresh
    Lesson objects via greedy first-fit matching. Surplus pinned rows
    from curriculum changes are silently dropped.
  - _build_factory(seconds) replaces the module-level factory so each
    job honours its tt_solution.seconds_limit override.
  - persist_solution writes lesson.pinned back so subsequent re-solves
    inherit it.

Frontend (studio-v2):
  - SolutionList grows three knobs in the create-form: Basieren auf
    (parent dropdown, only completed solutions, disabled when none),
    Sekunden-Limit (5-600), and the existing Name.
  - PlanView cells get a pin/unpin button with optimistic update and
    rollback on error. Pinned cells gain an amber ring.
  - types.ts + api.ts mirror the new fields; lessonsApi.pin(id, bool).
  - HelpPanel: collapsible 6-step Bedienungsanleitung explaining the
    setup-to-plan workflow. Anchored at the top of /stundenplan above
    the dev token banner.
  - page.tsx switches to the same gradient + animated-blob background
    used on /korrektur so /stundenplan stops looking like a slate-900
    test page.
  - JWT dev banner gets a step-by-step explanation of how to grab the
    token from DevTools and a non-blocking success indicator (no more
    alert()).

Tests:
  - school-service: 6 new validator cases for parent_solution_id +
    seconds_limit boundaries. 73 subtests total, all green.
  - studio-v2: mockSchoolApi adds PUT /lessons/:id/pin route. 5 new
    Playwright tests across two suites (parent-selector visibility +
    options, seconds-limit input, pin button render, pin-icon flip).
    Existing tests adjusted to the new help panel + JWT banner wording.

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

timetable-solver-service/app/runner.py

@@ -35,32 +35,48 @@ logger = logging.getLogger(__name__)
 
 _executor = ThreadPoolExecutor(max_workers=2)
 
-_solver_factory = SolverFactory.create(
-    SolverConfig(
-        solution_class=Timetable,
-        entity_class_list=[Lesson],
-        score_director_factory_config=ScoreDirectorFactoryConfig(
-            constraint_provider_function=define_constraints,
-        ),
-        termination_config=TerminationConfig(
-            spent_limit=Duration(seconds=settings.solver_seconds_limit),
-        ),
+def _build_factory(seconds: int) -> SolverFactory:
+    """One factory per solve so we can honour per-job timeout overrides.
+    Cheap to construct — the Java side caches what it can across builds."""
+    return SolverFactory.create(
+        SolverConfig(
+            solution_class=Timetable,
+            entity_class_list=[Lesson],
+            score_director_factory_config=ScoreDirectorFactoryConfig(
+                constraint_provider_function=define_constraints,
+            ),
+            termination_config=TerminationConfig(
+                spent_limit=Duration(seconds=seconds),
+            ),
+        )
     )
-)
 
 
-def _solve_sync(problem: Timetable) -> Timetable:
+def _solve_sync(problem: Timetable, seconds: int) -> Timetable:
     """Blocking solver call; runs in a worker thread."""
-    solver = _solver_factory.build_solver()
+    solver = _build_factory(seconds).build_solver()
     return solver.solve(problem)
 
 
+async def _fetch_solve_options(pool, solution_id: str) -> tuple[str | None, int]:
+    """Read parent_solution_id + seconds_limit from tt_solution."""
+    async with pool.acquire() as conn:
+        row = await conn.fetchrow("""
+            SELECT parent_solution_id::text, seconds_limit
+            FROM tt_solution WHERE id = $1
+        """, solution_id)
+    parent = row["parent_solution_id"] if row else None
+    limit = row["seconds_limit"] if row and row["seconds_limit"] else settings.solver_seconds_limit
+    return parent, int(limit)
+
+
 async def run_solve(solution_id: str, user_id: str) -> None:
     """Top-level async entry. Caller fires-and-forgets via BackgroundTasks."""
     pool = await get_pool()
     try:
+        parent_id, seconds = await _fetch_solve_options(pool, solution_id)
         await mark_running(pool, solution_id)
-        problem = await build_problem(pool, user_id)
+        problem = await build_problem(pool, user_id, parent_solution_id=parent_id)
 
         if not problem.lessons:
             await mark_failed(pool, solution_id,
@@ -76,7 +92,7 @@ async def run_solve(solution_id: str, user_id: str) -> None:
             return
 
         loop = asyncio.get_running_loop()
-        solved: Timetable = await loop.run_in_executor(_executor, _solve_sync, problem)
+        solved: Timetable = await loop.run_in_executor(_executor, _solve_sync, problem, seconds)
 
         score = solved.score
         hard = score.hard_score() if score else 0