release: bump 0.8.6 -> 0.8.7 (#263)

Version bump `0.8.6` → `0.8.7`.

### Added
- R binding: a *Getting started* vignette and a synthetic `sample_ohlcv` example dataset, giving new users a runnable, self-contained walkthrough and populating the R-universe Articles and Datasets tabs. The vignette's code is exercised in CI so a broken example is caught before the published build. (#262)

Bump touches the manual release touchpoints only; docs/webpage version strings are left to `sync-about.yml` on the tag.

bindings/node/package.json

@@ -1,6 +1,6 @@
 {
   "name": "wickra",
-  "version": "0.8.6",
+  "version": "0.8.7",
   "description": "Streaming-first technical indicators: incremental, fast, install-free. Node bindings powered by Rust.",
   "author": "kingchenc <support@wickra.org>",
   "main": "index.js",
@@ -47,12 +47,12 @@
     "node": ">= 18"
   },
   "optionalDependencies": {
-    "wickra-linux-x64-gnu": "0.8.6",
-    "wickra-linux-arm64-gnu": "0.8.6",
-    "wickra-darwin-x64": "0.8.6",
-    "wickra-darwin-arm64": "0.8.6",
-    "wickra-win32-x64-msvc": "0.8.6",
-    "wickra-win32-arm64-msvc": "0.8.6"
+    "wickra-linux-x64-gnu": "0.8.7",
+    "wickra-linux-arm64-gnu": "0.8.7",
+    "wickra-darwin-x64": "0.8.7",
+    "wickra-darwin-arm64": "0.8.7",
+    "wickra-win32-x64-msvc": "0.8.7",
+    "wickra-win32-arm64-msvc": "0.8.7"
   },
   "scripts": {
     "build": "napi build --platform --release",