app: Classes binder + Mind Dump — v0.5.0

Two new tabs in the Studio Notebook:

- 📚 Classes: a binder for courses, workshops, books, and video series.
  Each class has a subject, source, link, status (taking / want / done),
  a what-it's-about note, photos, handout files, and dated pages of
  class notes that can be edited in place.
- 💭 Mind Dump: idea capture filed by category (things to make — with a
  medium: clay / wood / silver / metal / mixed — marketing, packaging,
  display & booth, shop & site, other) with spark / trying / did it /
  parked status, sketch photos, one-tap 'make it a to-do', and filters.
  The Today jot box gains a 💭 idea chip; those land as 'unsorted' to
  file later.

Schema: Course, CoursePage, Idea (additive; prisma db push at boot).
Files tab now labels attachments that belong to a class.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/public/index.html

@@ -98,6 +98,8 @@
       <button data-v="pieces">🏺 Pieces</button>
       <button data-v="files">🗂️ Files</button>
       <button data-v="sourcing">🧭 Sourcing</button>
+      <button data-v="classes">📚 Classes</button>
+      <button data-v="ideas">💭 Mind Dump</button>
       <button data-v="notes">📒 Notes</button>
     </nav>
     <nav style="margin-top:18px"><button id="signout" style="font-size:13px">👋 sign out</button></nav>