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.

examples/node/package-lock.json

@@ -17,7 +17,7 @@
     },
     "../../bindings/node": {
       "name": "wickra",
-      "version": "0.8.6",
+      "version": "0.8.7",
       "license": "MIT OR Apache-2.0",
       "devDependencies": {
         "@napi-rs/cli": "^2.18.0"
@@ -26,12 +26,12 @@
         "node": ">= 18"
       },
       "optionalDependencies": {
-        "wickra-darwin-arm64": "0.8.6",
-        "wickra-darwin-x64": "0.8.6",
-        "wickra-linux-arm64-gnu": "0.8.6",
-        "wickra-linux-x64-gnu": "0.8.6",
-        "wickra-win32-arm64-msvc": "0.8.6",
-        "wickra-win32-x64-msvc": "0.8.6"
+        "wickra-darwin-arm64": "0.8.7",
+        "wickra-darwin-x64": "0.8.7",
+        "wickra-linux-arm64-gnu": "0.8.7",
+        "wickra-linux-x64-gnu": "0.8.7",
+        "wickra-win32-arm64-msvc": "0.8.7",
+        "wickra-win32-x64-msvc": "0.8.7"
       }
     },
     "node_modules/wickra": {