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/0036_diagnostics.up.sql

@@ -1,4 +1,4 @@
--- Device diagnostics / debug-reporting subsystem (M9).
+-- Device diagnostics / debug-reporting subsystem.
 --
 -- When an account has users.debug_mode_enabled = true, that account's
 -- client(s) stream a timeseries of device state here: connectivity +
@@ -8,12 +8,12 @@
 -- /admin/diagnostics view filters by account + device + time window and
 -- exports the slice as JSON for offline analysis.
 --
--- `kind` is a COARSE category gated by a CHECK whitelist; the finer
--- event discriminator + all event-specific fields live in the `payload`
--- jsonb. This keeps the enum small and stable so new event variants
--- don't require a migration (per the enum-CHECK-whitelist rule, only a
--- new *category* would). If you add a category here, mirror it in the
--- handler whitelist in internal/api/diagnostics.go.
+-- `kind` is a COARSE category gated by a CHECK whitelist; the finer event
+-- discriminator + all event-specific fields live in the `payload` jsonb. This
+-- keeps the enum small and stable so new event variants don't require a
+-- migration (only a new *category* would: a new CHECK value means swapping the
+-- constraint in the same migration). If you add a category here, mirror it in
+-- the handler whitelist in internal/api/diagnostics.go.
 --
 -- Two timestamps on purpose: occurred_at is the client device clock
 -- (when the event happened on the phone — may be skewed/wrong, e.g. in