docs: query comments say what each query selects and why, not how it came to be (#6277)

Rewrites the internal/db/queries comments to rule 32 and regenerates
dbq, whose doc comments and embedded SQL carry them. The bugs behind the
tiered mixes, the md5 order seed, the score bands and the round-robin
arms are restated as the constraint each one enforces; counts from one
library and stale cross-references are gone.

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

internal/db/dbq/notifications.sql.go

@@ -54,7 +54,7 @@ type InsertNotificationParams struct {
 	EmailWanted bool
 }
 
-// M489 notifications inbox (#726). Rows are written only through
+// Notifications inbox. Rows are written only through
 // internal/notifications.Notifier, which decides recipients and honours each
 // recipient's inbox preference before it reaches these.
 // email_wanted is the recipient's email channel for this kind as of now. A
@@ -122,7 +122,7 @@ type ListEmailPendingNotificationsRow struct {
 	ReadAsOf    pgtype.Timestamptz
 }
 
-// Email digest (#5346) ------------------------------------------------------
+// Email digest ------------------------------------------------------
 // Every unread, un-emailed row of a user who has an address, oldest first.
 // Read rows are never selected: the user has seen them, so they are not news.
 // read_as_of is the database's clock at the read, handed back to
@@ -348,7 +348,7 @@ type MarkAllNotificationsReadParams struct {
 // all read" queued offline and replayed later must not mark notices that
 // arrived in between, which the user never saw. A coalesced row that grew
 // since then is marked read with it: it arrived before they asked, and its
-// growth is a quiet update to a notice they had seen (M542).
+// growth is a quiet update to a notice they had seen.
 func (q *Queries) MarkAllNotificationsRead(ctx context.Context, arg MarkAllNotificationsReadParams) (int64, error) {
 	result, err := q.db.Exec(ctx, markAllNotificationsRead, arg.UserID, arg.UpTo)
 	if err != nil {
@@ -484,10 +484,10 @@ type UpsertCoalescedNotificationParams struct {
 // ten. Every coalesced kind's event is "N more happened", never a restated
 // total, so the row always says what is new since it was last read.
 //
-// created_at and emailed_at are left alone (M542): an update changes what the
-// notice says, not when it arrived. Moving created_at made the phone announce
-// it again and clearing emailed_at sent it again, so a notice the hourly
-// duplicate pass kept growing alerted every hour.
+// created_at and emailed_at are left alone: an update changes what the
+// notice says, not when it arrived. Moving created_at would make the phone
+// announce it again and clearing emailed_at would send it again, so a notice
+// that keeps growing would alert on every update.
 func (q *Queries) UpsertCoalescedNotification(ctx context.Context, arg UpsertCoalescedNotificationParams) (pgtype.UUID, error) {
 	row := q.db.QueryRow(ctx, upsertCoalescedNotification,
 		arg.UserID,