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/0032_playback_errors.up.sql

@@ -1,6 +1,6 @@
 -- Client-reported playback errors. Populated by clients when a track
 -- fails to play (zero duration, decode error, etc.); surfaced in the
--- admin /admin/playback-errors inbox so the operator can hide / delete
+-- admin /admin/playback-errors inbox so an admin can hide / delete
 -- / re-request the offending track.
 --
 -- resolved_at + resolved_by + resolution are NULL until an admin acts
@@ -10,8 +10,8 @@
 -- unresolved-queue lookup fast even as resolved history accumulates.
 --
 -- CHECK constraints on kind/resolution gate the enum values so client
--- typos can't pollute the data (per the standing rule about
--- enum-CHECK whitelists needing migrations).
+-- typos can't pollute the data; a new value means swapping the constraint
+-- in the same migration as the code that writes it.
 
 CREATE TABLE playback_errors (
     id          uuid PRIMARY KEY DEFAULT gen_random_uuid(),