Refactor UI reservation

[joonatank]

🛠️ Changelog

• Refactor new and edit reservation to use same Calendar picker component.
• Add: quick slot select to edit reservation.
• Fix: only include active applications when checking reservability.
• Fix: redirect after edit then toast (not the other way).
• Fix: updated Calendar Legend.
• Fix: improve performance in reservability checks when there are thousands of reservations.
• Refactor: cleanup HTML / CSS structure of reservation pages (single grid).
• Refactor: move inner JSX code to separate components / lists.
• Fix: add a check for reservation editability on edit page.
• Remove: touch device calendar hacks.

🧪 Test plan

• Manual testing: new reservation and edit reservation should work, and should be consistent (with all three controls).

🎫 Tickets

• TILA-3512
• TILA-3502