feat: vector provider identity is a required name field (hnsw-js), rendered [vector-index:<name>]

Reconciles the vector-index rename to the ruled three-layer naming: the
provider contract's identity field is now a REQUIRED readonly name (was
optional providerId), self-reported and truthful, rendered as
[vector-index:<name>] where the index identifies itself and stamped into
the op-name strings journals already parse (AddToVectorIndex(<name>)).
The built-in JS engine names itself hnsw-js. A runtime provider instance
compiled against the previous optional contract is tolerated - never
crashed on, never silently mislabeled: it stamps unknown-provider and
emits one loud warning naming the missing field. Graph index operations
keep their static names (they never interpolate provider identity), and
no public API exports a provider-routed hnsw-carrying name, so no
deprecation shim is required.

tests/unit/brainy/warm.test.ts

@@ -44,6 +44,7 @@ const V = (seed = 1): number[] => Array.from({ length: DIM }, (_, i) => Math.sin
  * `AddToVectorIndexOperation` / `brain.warm()` call through.
  */
 class FakeVectorProvider implements VectorIndexProvider {
+  readonly name = 'fake-vector-provider'
   readonly items = new Map<string, Vector>()
   warmCalls = 0
   searchCalls: Array<{ k?: number }> = []