Land Phase 1 of ADR-125. Public API now exports `MemoryService` as the
canonical entry point, with `UnifiedMemoryService` preserved as an
`@deprecated` alias (same class) until 3.0.0-rc.
Removed from the public surface:
- `HnswLite` — internal to RvfBackend; reachable via explicit module path.
- `RvfBackend` — selected through `createDatabase({ provider: 'rvf' })`.
Updates:
- `prepublishOnly` now requires `MemoryService` + `UnifiedMemoryService`
AND fails if `HnswLite` / `RvfBackend` re-appear on the top-level surface.
- New `src/index.test.ts` (7 tests) asserts the canonical surface.
- New `docs/migration-3.0.0-alpha.18.md` documents rename + deprecation.
No runtime behavior change. All 367 existing tests still pass; +7 new.
Refs: ADR-125 Phase 1, ADR-006, ADR-009
Closes: part of #2061
Co-Authored-By: RuFlo <ruv@ruv.net>
ruv