feat: extract MediaController, wire into Dispatcher, delete media.php

app/storage/migrations/006_add_composite_index.sql

@@ -0,0 +1,8 @@
+-- Migration 006: Add composite covering index (is_published, year DESC) on theses
+--
+-- Every public-facing query filters on is_published = 1 AND orders/filters by year.
+-- The existing separate idx_theses_published and idx_theses_year force the query
+-- planner to pick one index and sort the other via a temp B-tree.
+-- This single covering index eliminates the extra sort pass.
+
+CREATE INDEX IF NOT EXISTS idx_theses_pub_year ON theses(is_published, year DESC);