feat(8.0): wire the two cor-confirmed metadata-provider contract additions

Both shapes confirmed with cor for the lockstep (cor builds the native side
against these; the JS index is a no-op / unchanged):

- probeConsistency?(): Promise<boolean> — OPTIONAL O(1) cold-open consistency
  sampler on MetadataIndexProvider. brainy calls it ONCE per brain on the first
  read; on `false` it self-heals via detectAndRepairCorruption() — the metadata
  counterpart of the 7.33.2 graph cold-load guard, completing the phantom triad's
  detect-and-repair-on-open. Best-effort: a probe failure never breaks a read
  (the one-shot guard resets so a transient failure retries). The JS index omits
  the method, so it is simply never probed.

- getIdsForFilter(filter, opts?: { limit?; offset? }) — brainy passes a page
  bound on the UNSORTED find({ type, where, limit }) path so a native provider can
  early-stop and return only the [0, limit) prefix, killing the O(N) FFI marshal
  at billion scale (pairs with cor #75). brainy passes offset:0 and ALWAYS
  re-windows the result itself (visibility filter + slice); the JS index ignores
  opts and returns all matches (behaviour unchanged).

New unit tests cover brainy's call behaviour for both (probe→repair on false,
healthy→no-repair, failure-is-best-effort, once-per-brain; opts passed with
offset 0 on the unsorted path). Full gate green: unit 1718, integration 607.

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

src/utils/metadataIndex.ts

@@ -1788,9 +1788,12 @@ export class MetadataIndexManager implements MetadataIndexProvider {
   }
 
   /**
-   * Get IDs matching Brainy Field Operator metadata filter using indexes where possible
+   * Get IDs matching a Brainy Field Operator metadata filter using indexes where possible.
+   * The optional `_opts` page bound is part of the provider contract for the native
+   * index (early-stop at `offset+limit`); the JS index returns ALL matches and lets
+   * the caller window them, so `_opts` is intentionally ignored here.
    */
-  async getIdsForFilter(filter: any): Promise<string[]> {
+  async getIdsForFilter(filter: any, _opts?: { limit?: number; offset?: number }): Promise<string[]> {
     if (!filter || Object.keys(filter).length === 0) {
       return []
     }