feat(cli): tapir report — Stage-0 usage gate query

ActiveWeeks computes per-user distinct active weeks (reads login_events UNION
acts summary_actions) for the gate (VISION/ADR-016: usage in >=2 distinct
weeks). Because the user-owned tables are FORCE RLS under a non-superuser owner,
a single cross-user query is deny-all; instead it enumerates users from the
un-RLS'd identity map and counts each inside withUser — no privilege escalation,
no policy change.

`tapir report` prints the per-user table and the pass/fail verdict (needs only
TAPIR_DB_DSN). Pure formatter + store query are unit-tested, including the
cross-table shared-week dedup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/tapir/main.go

@@ -56,6 +56,8 @@ func main() {
 		err = cmdServe(ctx, log)
 	case "invite":
 		err = cmdInvite(ctx, os.Args[2:])
+	case "report":
+		err = runReport(ctx, os.Args[2:])
 	default:
 		usage()
 		os.Exit(2)
@@ -77,6 +79,7 @@ usage:
   tapir invite <email>    mint an invitation link for a new user (host-side)
   tapir list [-limit N]   list stored summaries, recent first
   tapir show <video-id>   show one summary in full
+  tapir report            Stage-0 usage gate: per-user distinct active weeks
 
 configuration is via TAPIR_* environment variables (see .env.example).
 `)