feat: add shared_notes schema and NoteShare types

Add sharedNotes table with noteId primary key, unique token, and
cascade delete. Add NoteShare and SharedNoteData interfaces.
Extend Note type with optional shareToken field.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

drizzle/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1773150888301,
       "tag": "0002_deep_black_widow",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "6",
+      "when": 1774037379518,
+      "tag": "0003_uneven_tomorrow_man",
+      "breakpoints": true
     }
   ]
 }