…y paths

Replaces five separate switch statements over the same 8 canonical op
types with a frozen Map<string, OpStrategy> registry. Each strategy
defines five methods: mutate, outcome, snapshot, accumulate, validate.

Adding a new op type without all five methods is a hard error at module
load time — the three apply paths (applyFast, applyWithReceipt,
applyWithDiff) can no longer diverge silently.

The public API is unchanged: applyFast, applyWithReceipt, applyWithDiff,
applyOpV2, join, reduceV5 all keep their exact signatures and semantics.

Includes cross-path equivalence tests verifying all three paths produce
identical CRDT state for every op type, multi-writer concurrency,
redundant ops, and the full reduceV5 pipeline.

5157/5157 tests pass. TSC zero. ESLint zero.