Complete Gate 2 source-connected aggregates

[hiroki23]

Summary

• pin the merged TypeRB snapshot v3 producer and connect it through the TypeRB-authored native driver
• add the Gate 2 source differential and reproducibility corpus for records, tagged values, Result/try, aggregate swaps, and explicit dynamic-storage rejection
• replace fixed-size libc copies with QBE blit and deterministic stores, then elide safe block-parameter copies while preserving parallel-copy semantics
• add the registered benchmark, raw measurements, and Gate 2 completion report

Results

• warm build time: 26.0% to 29.5% faster than the stronger applicable Go baseline
• runtime: two startup cases faster; five-million-iteration aggregate kernel 17.6% slower, within the 25% bound
• stripped executable size: 96.85% smaller
• observed build and runtime peak RSS: lower than both Go paths

Verification

• pinned TypeRB fmt --check .
• pinned TypeRB check for the repository, both benchmark tools, and all Gate 2 corpus configs
• 39 tests with QBE 1.3, including source differential, exact artifact reproducibility, and parallel aggregate swaps
• 10 build and 50 runtime observations per measured project; 726 successful measurements

Closes #7