Enhance weekly hours constraints and update documentation

[Vhivi]

This pull request introduces a new configurable weekly worked-hours cap to the solver, improves documentation, and adds robust validation and testing for this new feature. The default weekly cap is now set to 36 hours, and the constraint now properly counts all configured worked vacations, including night shifts. The change is reflected across the backend, configuration files, documentation, and tests.

Solver constraint and configuration improvements:

• Added solver.max_weekly_hours as a configurable weekly worked-hours cap per agent (default 36h), enforced in the solver and counted for all configured worked vacations, including night shifts. The constraint now uses this value instead of a hardcoded limit and is documented in the code and config files. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Documentation and changelog updates:

• Updated CHANGELOG.md and documentation files to describe the new weekly hours cap and clarify related configuration options. [1] [2] [3]

Validation and schema enhancements:

• Extended the configuration schema to support the new max_weekly_hours setting, requiring it to be a positive number, and updated example configs accordingly. [1] [2]

Testing improvements:

• Added and improved tests to verify that the weekly hours cap is enforced, including regression tests for night shift counting and parameterized tests for schema validation. [1] [2] [3]

Version bump:

• Bumped the version to 0.9.3 in both backend and frontend to reflect these changes. [1] [2]