chore(rules): drop the Redis payload rule until it has enforcement behind it

The transferable part of it — cap bytes, never entries — is real: three
independent writers made that exact mistake. But a rule pointing at a budget
module that two writers use and three ignore is prose, not a rule.

It belongs in `sim-caching.md`, trimmed to the part that transfers, alongside the
change that routes those writers through `redis-budget.server.ts`.

Author: waleedlatif1