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/0049_suggestion_snoozes.up.sql

@@ -1,14 +1,15 @@
 -- 0049_suggestion_snoozes.up.sql — time-boxed "not right now" on a Discover
--- artist suggestion (#2374, milestone #268 slice 3).
+-- artist suggestion.
 --
--- This is NOT a dislike. Rule #101 forbids a "Not for me" / thumbs-down /
--- exclusion UI, and a snooze deliberately isn't one: it records no verdict on
+-- This is NOT a dislike. Minstrel has no "Not for me" / thumbs-down /
+-- exclusion control — taste is learned from listening — and a snooze
+-- deliberately isn't one: it records no verdict on
 -- the music, expires on its own, and MUST NEVER feed the taste profile. It is
 -- acquisition triage — "I don't want to request this right now" — so the same
 -- candidate is free to return once snoozed_until passes. Anything that reads
 -- this table as negative preference signal is a bug.
 --
--- Per-user (rule #47), never global: one household member parking a
+-- Per-user, never global: one household member parking a
 -- suggestion must not remove it from anyone else's deck.
 --
 -- candidate_mbid is text with NO foreign key, on purpose. Suggestions come