style(audiobooks): uppercase PRIMARY KEY in migration 140

Aligns with the codebase convention (type keywords lowercase,
constraint keywords uppercase) established in migration 139's
post-style-fix form. Cosmetic only — running schema is unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations/140_podcast_feeds.up.sql

@@ -4,7 +4,7 @@
 -- episodes table.
 
 CREATE TABLE IF NOT EXISTS public.podcast_feeds (
-    media_item_id              text primary key
+    media_item_id              text PRIMARY KEY
                                REFERENCES public.media_items(content_id) ON DELETE CASCADE,
     feed_url                   text NOT NULL,
     etag                       text,