feat: add mobile weekly time blocking

[condyl]

Summary

• Add a visible mobile “Block time” action beside the schedule duration selector and in the empty schedule state.
• Add a weekly time editor with day chips, 30-minute time choices, optional name, and edit/delete flows for existing blocks.
• Reuse the existing time-block and timetable-generation logic.

Validation

• npm run lint passed.
• npm run build passed.
• Commit hook test run passed: 33 tests across 12 files.