v1.2.1

feat: improve subject management and refine schedule import logic

- Add a specific `codigo` (subject code) field to the schedule JSON distribution files and the `FlatScheduleSlot` data model.
- Update the import repository and parser to prioritize subject codes for matching and generate unique subject IDs using a combination of code and semester.
- Implement automatic semester switching during import when the schema or the imported subjects belong to a different cuatrimestre.
- Enhance the `AddEditSubjectScreen` with a clearer "View" mode, replacing the save icon with a text-based "Save" button and hiding the active toggle for new subjects.
- Add an inline "Add Slot" button to the empty state of the subject editor for a better user experience when creating subjects manually.
- Update `ScheduleViewModel` logic to show the auto-change semester tooltip if subjects exist in other semesters and the user has not yet performed a manual switch.
- Refactor `SemesterSwitcher` to allow flexible padding and ensure consistent layout across the schedule and subject list screens.
- Update localized string resources in English and Spanish to clarify manual entry buttons and improve slot management terminology.
- Update the Python parsing script to support the new subject code field in generated JSON files.