Implement favorites for notes (favorite action, filters, profile tab)

[joshuapanicker]

Summary
Add the ability to favorite notes, surface favorites in filters (e.g. course/dashboard browse), and show favorite notes in the profile page Favorites tab.

Current state

• Profile page has a Favorites tab with placeholder copy: "No favorites yet. Favorites coming soon."
• No favorite/unfavorite action exists on note cards or in note modals.
• No "favorites" filter or filter option in browse/course views.

Acceptance criteria

Data / backend

• Add persistence for favorites (e.g. note_favorites or resource_favorites table with profile_id, resource_id, or use existing schema if one exists).
• API (or extend existing /api/notes) to support:
  • Toggle favorite (add/remove) for the current user.
  • Listing notes filtered by "favorited by me" (e.g. favorited=1 or dedicated endpoint).

UI – favoriting

• Add a way to favorite/unfavorite a note (e.g. star icon on note cards and/or in the note detail modal).
• Indicate favorited state visually (e.g. filled star vs outline).

UI – filters

• In browse/course views, add a filter or tab to show "Favorites" (notes the user has favorited).
• Ensure favorited notes can be discovered and opened from this view.

UI – profile

• In the profile page Favorites tab, fetch and display the user’s favorited notes (same card style as My Uploads / Downloads).
• Empty state: keep friendly message when the user has no favorites.
• Each card should link to the relevant course/note context (e.g. course page) where applicable.

Notes

• Reuse existing note card and list patterns (e.g. profile uploads/downloads, course detail) for consistency.
• Consider RLS and auth so users only see and modify their own favorites.