fix: SONA zero-vector bug, RVF wasm persistence, metadata safety, doc gaps (#708)

- #706: apply_micro_lora/apply_base_lora seeded their output buffer with
  zeros in napi.rs, napi_simple.rs, and wasm.rs, but the Rust LoRA forward
  pass has residual semantics (adds delta into the buffer). Cold queries
  collapsed to the zero vector, and post-feedback queries returned only
  the delta instead of input+delta. Fixed by seeding with a clone of the
  input in all three binding layers. Added regression tests.

- #705: WasmBackend had no byte-level persistence. The underlying
  rvf_store_export/rvf_store_open C-ABI functions already existed —
  wired them into WasmBackend.exportBytes()/openBytes() and
  RvfDatabase.exportBytes()/openBytes(), verified against the real
  compiled .wasm binary.

- #704: NodeBackend.ingestBatch() silently dropped RvfIngestEntry.metadata
  instead of forwarding it, and query() filter serialization omitted the
  native parser's required valueType. Since a full field-name-to-id
  design for metadata durability is a larger follow-up, applied the
  issue's own suggested interim fix: ingest now throws
  MetadataNotSupported instead of silently losing data. Filter
  serialization now infers and includes valueType.

- #707: docs/api/NODEJS_API.md and docs/guides/ADVANCED_FEATURES.md
  advertised HybridSearch/FilteredSearch/MMRSearch/ConformalPredictor as
  Node exports; none are bound by crates/ruvector-node. Corrected with
  explicit "not yet shipped" notes pointing at the tracking issue.

README corrections for #705/#707 (WasmRvfStore, HybridSearch docs) are
staged separately — a repo hook requires a visual design-grade ritual for
any README change that this session cannot complete (no browser/screenshot
access), so they'll follow once that's resolved.

docs/api/NODEJS_API.md

@@ -607,10 +607,21 @@ interface QuantizationConfig {
 
 ## Advanced Features
 
-### HybridSearch
+> **Not yet available in the `ruvector` Node package.** `HybridSearch`,
+> `FilteredSearch`, and `MMRSearch` below exist in the Rust core
+> (`ruvector-core::advanced_features`) but are **not bound or exported** by
+> `crates/ruvector-node` / the published `ruvector` npm package — see
+> [#707](https://github.com/ruvnet/RuVector/issues/707). Importing any of
+> these names from `ruvector` in Node.js currently returns `undefined`.
+> If you need hybrid/keyword search from JavaScript today, use AgentDB's
+> `HybridSearch` / `KeywordIndex` (`ruvnet/agentdb`) instead. The snippets
+> below describe the intended shape of a future Node binding, not a
+> currently shipped API.
+
+### HybridSearch (Rust-only; not exported to Node)
 
 ```javascript
-const { HybridSearch } = require('ruvector');
+const { HybridSearch } = require('ruvector'); // NOT YET SHIPPED — see #707
 
 const hybrid = new HybridSearch(db, {
     vectorWeight: 0.7,
@@ -626,10 +637,10 @@ const results = await hybrid.search(
 );
 ```
 
-### FilteredSearch
+### FilteredSearch (Rust-only; not exported to Node)
 
 ```javascript
-const { FilteredSearch } = require('ruvector');
+const { FilteredSearch } = require('ruvector'); // NOT YET SHIPPED — see #707
 
 const filtered = new FilteredSearch(db, 'preFilter');
 
@@ -641,10 +652,10 @@ const results = await filtered.search(queryVector, 10, {
 });
 ```
 
-### MMRSearch
+### MMRSearch (Rust-only; not exported to Node)
 
 ```javascript
-const { MMRSearch } = require('ruvector');
+const { MMRSearch } = require('ruvector'); // NOT YET SHIPPED — see #707
 
 const mmr = new MMRSearch(db, {
     lambda: 0.5,