Make old migration that depends on the sqlite vec0 module a no-op

Once the sqlite 'vec0' module was removed from the codebase in
38a7a144 (following the table removal in 875a298f), this migration
became unrunnable. So to make sure we can reconstruct the schema if
necessary by running all the migrations, I'm replacing it with the
creation of an empty table.

db/migrate/20250723165724_create_search_embeddings.rb

@@ -1,10 +1,16 @@
 class CreateSearchEmbeddings < ActiveRecord::Migration[7.1]
   def change
-    create_virtual_table :search_embeddings, :vec0, [
-      "id INTEGER PRIMARY KEY",
-      "record_type TEXT NOT NULL",
-      "record_id INTEGER NOT NULL",
-      "embedding FLOAT[1536] distance_metric=cosine"
-    ]
+    # create_virtual_table :search_embeddings, :vec0, [
+    #   "id INTEGER PRIMARY KEY",
+    #   "record_type TEXT NOT NULL",
+    #   "record_id INTEGER NOT NULL",
+    #   "embedding FLOAT[1536] distance_metric=cosine"
+    # ]
+
+    # Above is the original migration. Once the sqlite 'vec0' module was removed from the codebase
+    # in 38a7a144 (following the table removal in 875a298f), this migration became unrunnable. So to
+    # make sure we can reconstruct the schema if necessary by running all the migrations, I'm
+    # replacing it with this empty table.
+    create_table :search_embeddings
   end
 end