chore: drop CF→AWS migration tooling and stale JS-port references

The CF→AWS data migration (closed 2026-05-16) is long done and the
tooling isn't wired into any production path. Remove the one-shot binary,
its support package, and the migration runbook.

In live code, replace 'JS-parity' / 'same shape as JS' / 'cross-runtime
KV migration' comments with the real, stable reason for each behavior
(wire-format invariant, null-vs-zero distinction, CloudWatch alarm field
name, etc.). 24 files touched across lolschedule, loldle, wordle, twentyq,
trading, misc, util, server, metrics, ai, keylock.

- delete cmd/migrate_cf_data/
- delete internal/migration/
- delete docs/cf-to-aws-migration-runbook.md

internal/server/log_middleware.go

@@ -36,7 +36,7 @@ func (r *statusRecorder) effectiveStatus() int {
 //	{"msg":"req","method":"POST","path":"/webhook","status":200,"ms":12}
 //
 // CloudWatch Logs filters on `jsonPayload.msg=req AND jsonPayload.status>=500`
-// for 5xx-rate alerting. Mirrors the JS source's index.js shape.
+// for 5xx-rate alerting — keep the field names stable or the alarm goes dark.
 //
 // The req line is emitted from a deferred closure so a panic in a downstream
 // handler still produces an observable log entry — without this, a cron