docs(perf): spec 034 element allocation reduction + investigation (#124)

Spec 034 locks in three production-ready perf changes (EX1 MemoCells with
explicit deps, EX3 direct-record-initializer idiom, EX4 bucketed
ElementModifiers via shim) drawn from a same-day measured A/B
investigation. EX2 (inline fluent fast paths) dropped as a measured
regression. Measured strongest combination beats unmodified Reactor by
+51 percent renders and Direct by +32 percent on the 4,900-cell 10 percent
mutation workload.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: codemonkeychris