perf(sponsors): add indexes and fragment caching for sponsors page

app/views/shared/_sponsor.html.haml

@@ -0,0 +1,2 @@
+.col-4.col-md-3.col-lg-2.mt-4.d-flex.justify-content-center
+  = link_to image_tag(sponsor.avatar.url, alt: sponsor.name, class: 'small-image mw-100'), sponsor.website, title: sponsor.name, class: 'border-0 mw-100'

app/views/shared/_sponsors.html.haml

@@ -1,4 +1,2 @@
 .row.d-flex.align-items-center.justify-content-center
-  - sponsors.each do |sponsor|
-    .col-4.col-md-3.col-lg-2.mt-4.d-flex.justify-content-center
-      = link_to image_tag(sponsor.avatar.url, alt: sponsor.name, class: 'small-image mw-100'), sponsor.website, title: sponsor.name, class: 'border-0 mw-100'
+  = render partial: 'shared/sponsor', collection: sponsors, as: :sponsor, cached: true

db/migrate/20260810091618_add_indexes_to_sponsors_for_active_and_search.rb

@@ -0,0 +1,15 @@
+class AddIndexesToSponsorsForActiveAndSearch < ActiveRecord::Migration[8.1]
+  disable_ddl_transaction!
+
+  def change
+    add_index :sponsors, :updated_at,
+              order: { updated_at: :desc },
+              where: 'level <> 0',
+              algorithm: :concurrently,
+              if_not_exists: true
+
+    add_index :sponsors, 'lower(name)',
+              algorithm: :concurrently,
+              if_not_exists: true
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_06_000000) do
+ActiveRecord::Schema[8.1].define(version: 2026_08_10_091618) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -512,6 +512,8 @@
     t.integer "seats", default: 15
     t.datetime "updated_at", precision: nil
     t.string "website"
+    t.index "lower((name)::text)", name: "index_sponsors_on_lower_name"
+    t.index ["updated_at"], name: "index_sponsors_on_updated_at", order: :desc, where: "(level <> 0)"
   end
 
   create_table "sponsorships", id: :serial, force: :cascade do |t|