add LIKE substring fallback to search and update plan statuses

FTS5 prefix matching misses mid-word substrings (e.g. "ebook" in
"notebook"). When FTS5 returns zero results, fall back to LIKE
query on title and category with proper wildcard escaping. 4 new
tests, 757 total.

Also marks completed plan files (search, admin-redesign,
setup-wizard, products-context) with correct status.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/simpleshop_theme/search.ex

@@ -27,7 +27,11 @@ defmodule SimpleshopTheme.Search do
       []
     else
       fts_query = build_fts_query(query)
-      search_fts(fts_query)
+
+      case search_fts(fts_query) do
+        [] -> search_like(query)
+        results -> results
+      end
     end
   end
 
@@ -135,6 +139,26 @@ defmodule SimpleshopTheme.Search do
     end
   end
 
+  # Substring fallback when FTS5 prefix matching returns nothing
+  defp search_like(query) do
+    pattern = "%#{sanitize_like(query)}%"
+
+    Product
+    |> where([p], p.visible == true and p.status == "active")
+    |> where([p], like(p.title, ^pattern) or like(p.category, ^pattern))
+    |> order_by([p], p.title)
+    |> limit(20)
+    |> preload(^@listing_preloads)
+    |> Repo.all()
+  end
+
+  defp sanitize_like(input) do
+    input
+    |> String.replace("\\", "\\\\")
+    |> String.replace("%", "\\%")
+    |> String.replace("_", "\\_")
+  end
+
   defp insert_into_index(%Product{} = product) do
     Repo.query!(
       "INSERT INTO products_search_map (product_id) VALUES (?1)",