Fixed darkening issues

Improvements:
- Bus departure columns now stay in fixed alphabetical order (no more swapping between refreshes)
- Departures within each line sorted earliest-first ("Now" always at top)
- Delayed buses now show delay amount, e.g. "5 min (+3)"
- Smart polling: pauses when the tab is in the background, polls less often when buses are far away
- Per-user daily rate limiting to ensure reliable service for all users
- Left accent bar changed to DTU red

v2.0 — DTU After Dark

New features:
- Live bus departure times for DTU-area stops (150S, 300S, 40E, 15E, 193) powered by Rejseplanen
- Configurable bus lines and directions via setup wizard
- Extension renamed from "DTU Dark Mode" to "DTU After Dark"
- GPA calculation with hyptothetical future grades included
- Content shortcut directly via DTU Learn homepage

Improvements:
- Onboarding hint now shows for the first 3 homepage visits to help new users find the settings
- Updated privacy policy to reflect Rejseplanen API usage
- Darkening fixes
- Misc. fixes

Added full dark mode support for campusnet.dtu.dk, frontpage, grades, sidebar, widgets, and participants are now themed. Includes a weighted GPA calculator (ECTS-weighted) on CampusNet grade pages. Improved styling for Brightspace settings pages, tab panels, and page headers.