feat: add storage budgeting and audit pipeline utilities

[preshotta]

Summary

• add deterministic tenant-hash monthly partition planning and DDL generation
• add Soroban storage/rent budget estimation utilities for comparing layouts
• add a bounded client-side ZK proof cache with TTL and LRU eviction
• add a contract audit event streamer with cursoring, normalization, and dedupe
• document the storage, proof-cache, and audit pipeline

Closes #524
Closes #525
Closes #526
Closes #527

Testing

• node --input-type=module -e "...module checks..."
• git diff --check

Note: npx vitest run test/partitioning.test.js test/soroban-storage-budget.test.js test/zk-proof-cache.test.js test/audit-streamer.test.js could not start because this fresh clone had no node_modules; npm ci is blocked because package.json and package-lock.json are already out of sync, and this host is Node v24 while the repo declares Node 22.x.

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