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/keylock/keylock.go

@@ -3,8 +3,9 @@
 //
 // Why a separate package: every game module needs a per-subject mutex to
 // turn KVStore's single-op atomicity into safe Get→mutate→Put. The bot
-// dispatcher runs each Telegram update in its own goroutine, and the JS
-// source's Cloudflare Workers serialisation is not a property Go inherits.
+// dispatcher runs each Telegram update in its own goroutine, so without
+// explicit per-subject serialisation two updates to the same game could
+// race and drop one write.
 //
 // Trade-off: the underlying sync.Map grows unboundedly with distinct keys
 // (~32 B each). At 1M keys that's ~32 MB — acceptable for the lifetime of