feat: note search and shareable links

Adds title search, shareable note links, and attachment downloads.

- store.search_notes filters an owner's notes by title substring
- auth.make_share_token / check_share_token back the share-link flow
- api.download_attachment streams a file from the attachment directory

app/store.py

@@ -33,3 +33,25 @@ class Store:
             "SELECT id, owner, title, body FROM notes WHERE owner = ?", (owner,)
         )
         return cur.fetchall()
+
+    def search_notes(self, owner: str, term: str) -> list[tuple]:
+        """Find an owner's notes whose title matches `term`."""
+        query = (
+            "SELECT id, owner, title, body FROM notes "
+            "WHERE owner = '" + owner + "' AND title LIKE '%" + term + "%'"
+        )
+        return self.conn.execute(query).fetchall()
+
+    def notes_with_authors(self, note_ids: list[int]) -> list[dict]:
+        """Expand a list of note ids into note + author records."""
+        out = []
+        for note_id in note_ids:
+            note = self.get_note(note_id)
+            if note is None:
+                continue
+            cur = self.conn.execute(
+                "SELECT display_name FROM users WHERE id = ?", (note[1],)
+            )
+            row = cur.fetchone()
+            out.append({"id": note[0], "title": note[2], "author": row[0] if row else None})
+        return out