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/java/README.md

@@ -30,14 +30,14 @@ Maven:
 <dependency>
   <groupId>org.wickra</groupId>
   <artifactId>wickra</artifactId>
-  <version>0.8.6</version>
+  <version>0.8.7</version>
 </dependency>
 ```
 
 Gradle:
 
 ```kotlin
-implementation("org.wickra:wickra:0.8.6")
+implementation("org.wickra:wickra:0.8.7")
 ```
 
 The native library ships prebuilt per platform (Linux, macOS, Windows — x64 and

bindings/java/pom.xml

@@ -6,7 +6,7 @@
 
   <groupId>org.wickra</groupId>
   <artifactId>wickra</artifactId>
-  <version>0.8.6</version>
+  <version>0.8.7</version>
   <packaging>jar</packaging>
 
   <name>Wickra</name>