feat(docs): add detailed planning objectives and optimization rules documentation

docs/adr/0003-constraint-first-lexicographic-planning.md

@@ -2,4 +2,6 @@
 
 The ten-second automatic deadline is superseded by [ADR 0006](0006-user-selected-horizons-and-cancellable-calculations.md), implemented by issue #59. Technical callers can still opt into an explicit planning-work budget; the user flow has no automatic cutoff.
 
+The fixed ordering between user preferences and configurable optimization objectives, including the unconditional priority for at-risk loss prevention, is superseded by [ADR 0008](0008-user-controlled-planning-objectives.md); implementation of that decision is pending.
+
 VacOptimizer resolves obligation rules exactly and jointly, then applies deterministic heuristic stages for at-risk loss, ordered preferences, complete public-holiday weeks, calendar gain, work-sequence quality, supporting placements, balance expiry, and dates in that order; complete holiday weeks therefore precede broader calendar-gain and work-sequence optimization. A completed plan does not claim mathematical global optimality. The dependency-free planner targets five seconds, returns `PlanningIncomplete` if those stages are interrupted, and stops after ten seconds. A HiGHS WebAssembly spike missed that hard limit on representative inputs even on the development machine, so no solver dependency is accepted. This supersedes ADR 0001.