fix(traces): review fixes for trace_iatas

Refresh last_heard on duplicate observations too, capped at hourly, so
steady traffic can't age a trace out of the filter (dedup key has no
heard_at). Drop the unused last_heard index column so upserts stay HOT,
and share one retention cutoff across the cleanup deletes.

db/sqlc/querier.go

@@ -236,6 +236,7 @@ type Querier interface {
 	UpsertPacket(ctx context.Context, arg UpsertPacketParams) (UpsertPacketRow, error)
 	UpsertRegion(ctx context.Context, arg UpsertRegionParams) (int32, error)
 	UpsertRegionIATA(ctx context.Context, arg UpsertRegionIATAParams) error
+	// Refreshes at most hourly so repeat hears don't churn the row.
 	UpsertTraceIATA(ctx context.Context, arg UpsertTraceIATAParams) error
 	// ============================================================
 	// TRANSPORT CODES

db/sqlc/queries.sql.go

@@ -4072,7 +4072,8 @@ const upsertTraceIATA = `-- name: UpsertTraceIATA :exec
 INSERT INTO trace_iatas (trace_tag, iata, last_heard)
 VALUES ($1, $2, $3)
 ON CONFLICT (trace_tag, iata) DO UPDATE SET
-  last_heard = GREATEST(trace_iatas.last_heard, EXCLUDED.last_heard)
+  last_heard = EXCLUDED.last_heard
+WHERE EXCLUDED.last_heard > trace_iatas.last_heard + INTERVAL '1 hour'
 `
 
 type UpsertTraceIATAParams struct {
@@ -4081,6 +4082,7 @@ type UpsertTraceIATAParams struct {
 	LastHeard pgtype.Timestamptz `json:"last_heard"`
 }
 
+// Refreshes at most hourly so repeat hears don't churn the row.
 func (q *Queries) UpsertTraceIATA(ctx context.Context, arg UpsertTraceIATAParams) error {
 	_, err := q.db.Exec(ctx, upsertTraceIATA, arg.TraceTag, arg.Iata, arg.LastHeard)
 	return err