React with pi's digits on pi day

We already generate 🥧 emoji reactions to "Good Morning" messages on pi day, i.e. March 14, maybe we could extend this mechanism to also react with a new digit for each message sent (per channel). One approach for generating these are streaming Spigot algorithms, which we could even move into a separate Swift package, if we have a nice implementation, potentially under an `IteratorProtocol` interface. Once we have that, we could even add other irrational/transcendental numbers that are easy to generate.

Start by locating the existing March 14 mechanism that reacts to “Good Morning” messages with 🥧, then trace how messages and channels are handled. Clarify whether digit generation belongs in the existing code or a separate Swift package, and define how per-channel state, IteratorProtocol integration, and completion criteria should work before implementing.

Written by the indexing model from the issue text.