feat(storage): add research project store

[hubab1]

Summary

• add an actor-isolated research-project store returning immutable Sendable snapshots
• implement project create/list/update/delete and keyword membership list/add/remove
• enforce UTF-8 bounds, strict storefronts, deterministic paging, 100-project and 500-keyword caps
• use incarnation-aware optimistic revisions so stale handles cannot mutate recreated rows
• preserve shared query, ranking, metric, and difficulty evidence when memberships or projects are deleted
• expose only a read-only research-store protocol to MCP

Current-main integration

The store commit was reconstructed after the V5 schema merged. Production MCP continues to use the shared provider pipeline and web-first ranking factory; the new injectable runtime seam preserves those dependencies while adding only the read-only research store.

Validation

• focused store, dependency, MCP service, and MCP protocol suites passed
• full project suite: 487 tests passed
• concurrent adds, idempotency, stale revisions, reopen behavior, and shared-data preservation are covered
• Swift 6.2 complete strict-concurrency build passed
• Xcode project validation and git diff --check passed

Scope

This PR adds lifecycle/storage services only. It exposes no research UI or MCP mutation tool.

Contributes to #3.