feat: add PlanningDurationService for estimating planning duration

- Implemented PlanningDurationService to provide an indicative wait time before calculation based on user input and calendar settings.
- Introduced duration estimation logic that considers horizon dates, balances, and rules without triggering a calculation.
- Enhanced user input component to display estimated duration using the new service.
- Updated translation files to include new duration estimate strings in multiple languages.
- Added tests for PlanningDurationService to ensure accurate duration estimation and calibration.
- Refactored leave planner service to remove hardcoded deadlines and improve worker responsiveness.

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

@@ -1,5 +1,5 @@
 # Constraint-First Lexicographic Planning Without a Solver Dependency
 
-The ten-second automatic deadline is superseded by [ADR 0006](0006-user-selected-horizons-and-cancellable-calculations.md), accepted for issue #12 and awaiting implementation.
+The ten-second automatic deadline is superseded by [ADR 0006](0006-user-selected-horizons-and-cancellable-calculations.md), implemented by issue #59.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.
 
 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.