Show favorites across all days when current day has none

[JacobCoffee]

Summary

• When viewing favorites on a day with none, detects if other days have favorites
• Shows contextual "No favorites on [Day]" message with "Show favorites on other days" button
• Combines all days' favorites into a single list with day-labeled group headers

Closes PYMOBIL-2

Test plan

• Favorite sessions on multiple days (e.g. Fri, Sat, Sun)
• Switch to a day with no favorites — verify "No favorites on [Day]" message appears
• Tap "Show favorites on other days" — verify all favorites from all days shown with correct day labels
• Switch to a day with no favorites and no favorites anywhere — verify "No favorites yet" message
• Tap day tabs to exit all-days mode — verify normal single-day view resumes

🤖 Generated with Claude Code

[linear]

PYMOBIL-2 Search and Favorites should show results across all days