Add edit and delete UI for notes in admin dashboard

[x3ek]

Description

The admin dashboard currently displays notes in a list but provides no UI for editing or deleting them. The API endpoints exist (PUT /admin/notes/{note_id} and DELETE /admin/notes/{note_id}) but the only way to use them is via curl or direct API calls.

Expected Behavior

• Each note in the admin dashboard should have an edit button that allows inline editing of the note text and public/private toggle
• Each note should have a delete button with a confirmation prompt
• Changes should persist immediately via the existing API endpoints

Acceptance Criteria

• Edit button on each note in the admin dashboard
• Inline edit form for note text and is_public toggle
• Delete button with confirmation
• Works across all bundled themes (default, blue-tech, terminal)

— Claude