docs: migration headers keep the before and after, without ids, quotes or one library's numbers (#6277)

Applies rule 32's migration exception: each header still says what the
schema was, what changes and what it prevents, but task, milestone,
decision and rule ids are replaced by the practice they stood for, the
operator quotes by the decision, single-install counts are dropped, and
pointers to a deleted package and an external design doc are gone.
golang-migrate keeps no checksum, so editing applied migrations'
comments is safe.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/migrations/0013_lidarr_metadata_profile.up.sql

@@ -1,9 +1,8 @@
--- M6a follow-up: persist the operator's metadata-profile choice alongside
--- quality profile + root folder. Lidarr POST /api/v1/artist requires
--- metadataProfileId; without storing it we'd refetch and pick first on
--- every Approve, denying the operator a choice. Nullable: existing rows
--- (and operators upgrading from before this migration) get NULL and the
--- service falls back to "fetch list and pick first" until they save.
+-- Persist the chosen Lidarr metadata profile alongside quality profile +
+-- root folder. Lidarr POST /api/v1/artist requires metadataProfileId;
+-- without storing it every Approve would refetch and pick the first.
+-- Nullable: existing rows get NULL and the service falls back to "fetch
+-- list and pick first" until an admin saves.
 
 ALTER TABLE lidarr_config
     ADD COLUMN default_metadata_profile_id integer;