Fix: Star icon removes rooms from sidebar when toggled in room view

[yashranaway]

Fixes the bug where clicking the star icon from the room view would hide the room from both "My Rooms" and "All Rooms" sections.

Campfire originally had a feature to hide rooms (invisible state), but since we have the star system for organizing rooms, this feature is no longer needed and was causing confusion.

Changes:

• Removed invisible from involvement cycle - star icon now only toggles between mentions (All Rooms) and everything (My Rooms)
• Removed all UI/CSS references to invisible state from navbar and profile page
• Changed thread room default involvement from invisible to mentions for non-creators
• Deleted unused notification-bell-invisible.svg icon

Technical Details:

• Database enum still contains invisible for backward compatibility
• Controller logic for handling invisible state remains for existing data
• Users can no longer manually set rooms to hidden via any UI element

Screen.Recording.2025-10-19.at.10.43.35.AM.mov

[yashranaway]

@dvassallo hey please take a look