feat(storage): add persistent UUID membership indexes for bounded ingest validation

[DecisionNerd]

Problem

Bulk edge validation currently rebuilds in-memory sets of all persisted node UUIDs, and publication checks can load all edge UUIDs. Repeated O(V/E) scans and unbounded sets cannot support billion-edge staged ingest.

Objective

Provide authoritative persistent UUID membership indexes that allow bounded-memory node and edge existence checks without changing UUID semantics.

Requirements

• Define the on-disk index format, versioning, checksums, atomic publication, and reopen behavior.
• Support batched membership probes and duplicate detection for node and edge UUIDs.
• Build or update indexes transactionally with graph publication.
• Detect missing, stale, or corrupt indexes and fail safely or rebuild through an explicit bounded path.
• Preserve Rust ownership; bindings consume the public facade only.
• Expose useful probe/build metrics without leaking graph data.

Acceptance criteria

• Edge validation no longer requires materializing every persisted node UUID.
• Publication duplicate checks no longer require materializing every persisted edge UUID.
• Peak index-build/probe memory is bounded by configured batch/work limits.
• Reopen, crash-before-publish, corruption, and concurrent-reader tests are deterministic.
• Index contents reconcile with canonical graph counts and UUID lookup behavior.
• Format/version documentation and migration/rebuild behavior are documented.

Scenarios

• Given a batch whose endpoints are partly missing, when membership is probed, then missing UUIDs are reported deterministically without loading the full vertex set.
• Given a crash before the new index manifest is published, when the project reopens, then readers observe the prior valid index and graph.
• Given an index checksum mismatch, when the graph opens, then GraphForge returns a typed integrity error and never silently accepts stale membership.

Non-goals

A general secondary-index framework or foreign key engine.

Related issues

Canonical tracker: #735. Direct prerequisite: #736.