refactor(8.0): API-surface + quality polish from the readiness audit

- find() search-mode: collapsed the two overlapping options to one canonical
  `searchMode: SearchMode` (the redundant `mode` alias was silently ignored on
  the primary find() path while honored on the historical path — a footgun) and
  removed the unwired `explain?` FindParams field (never read by find()).
- Documentation accuracy on the public type surface: entity ids documented as
  UUID v7 (auto) / v5 (natural key), not v4; dropped the stale "Brainy 3.0"
  banners and "backward compatibility" hedging on the fresh-8.0 Result type;
  documented the via/type alias; removed the dead GraphConstraints.bidirectional;
  fixed the no-op `EmbeddedGraphVerb = Omit<GraphVerb,'source'>` to omit the real
  sourceId; corrected the GraphIndexProvider.isInitialized JSDoc; documented
  removeMany's per-chunk generation granularity; JSDoc'd the public VFS surface.
- Honest perf comments in source: removed unmeasured billion-scale figures from
  the LSMTree / graphAdjacencyIndex headers (the JS fallback is in-memory after
  open; native is the scale path).
- Robustness: getVerbMetadata propagates read errors symmetrically with
  getNounMetadata; the find() egress integrity-guard keeps a row when the JS
  matcher doesn't implement an operator the provider already matched on; hardened
  the boundary-no-native CI guard to catch side-effect imports + re-exports.
- Tests: de-theatricalized a relateMany test to assert the real contract; fixed
  a stale Model-B header.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/plugin.ts

@@ -219,7 +219,13 @@ export interface MetadataIndexProvider {
  * contract at this surface.
  */
 export interface GraphIndexProvider {
-  /** `false` until the index has loaded; Brainy probes this before fast paths. */
+  /**
+   * `false` until the provider has loaded its persisted state. A provider should
+   * self-load on first read; this flag lets it report readiness for diagnostics
+   * and tooling. (Brainy's graph reads route through the provider's own methods,
+   * which are expected to be self-loading — it is the {@link GraphAccelerationProvider}
+   * fast paths that gate on `isInitialized`.)
+   */
   readonly isInitialized: boolean
 
   /**