Add competitor-discovery search (/discover)

The actual "who sells honey with a .es domain" feature: search sites
by keyword — matched against page title/description/keywords/body
text via a new MySQL fulltext index on site_pages — combined with an
optional TLD filter on the domain. Results are sites ranked by number
of matching pages. Shows nothing until a filter is entered, so it
doesn't just duplicate the plain Sites browse page.

Verified against real .es data pulled in for the test (dominio ->
4 matching sites, correctly ranked and TLD-filtered).

database/migrations/2026_07_22_211812_add_fulltext_index_to_site_pages_table.php

@@ -0,0 +1,29 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Backs the product/keyword search used by the discovery page — matching a term
+     * like "honey" against a page's title/description/keywords/body text.
+     */
+    public function up(): void
+    {
+        Schema::table('site_pages', function (Blueprint $table) {
+            $table->fullText(['title', 'description', 'keywords', 'content']);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('site_pages', function (Blueprint $table) {
+            $table->dropFullText(['title', 'description', 'keywords', 'content']);
+        });
+    }
+};