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/0071_reopen_false_reacquisition_completions.up.sql

@@ -1,10 +1,10 @@
--- #5263: the reconciler completed album and track requests as soon as the album
--- had any track on disk. Re-acquisition targets albums with only SOME tracks
--- missing, so those requests completed the moment Lidarr accepted the add,
--- with nothing downloaded.
+-- Before: the reconciler completed album and track requests as soon as the
+-- album had any track on disk. Re-acquisition targets albums with only SOME
+-- tracks missing, so those requests completed the moment Lidarr accepted the
+-- add, with nothing downloaded.
 --
 -- Reopen every completed album/track request whose matched album does not meet
--- the corrected test (see albumForRequest in internal/lidarrrequests): a track
+-- the corrected test: a track
 -- that arrived after the request, or no track that was already missing at the
 -- request still missing. The reconciler then judges them again; the Lidarr add
 -- stays confirmed, so nothing is re-sent. Requests that genuinely completed