release: bump 0.8.5 -> 0.8.6 (#260)

Version bump `0.8.5` → `0.8.6`.

### Changed
- Package registry metadata for better discoverability (#259):
  - R (R-universe): R-universe URL + `X-schema.org-keywords` in `DESCRIPTION`, package logo at `bindings/r/man/figures/logo.png`.
  - Python (PyPI): `Documentation` project URL.
  - C# (NuGet): package icon via `PackageIcon`.

Ships the metadata so the next PyPI/NuGet publish carries the new fields (R-universe rebuilds from main independently). 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>0.8.5</version>
+  <version>0.8.6</version>
 </dependency>
 ```
 
 Gradle:
 
 ```kotlin
-implementation("org.wickra:wickra:0.8.5")
+implementation("org.wickra:wickra:0.8.6")
 ```
 
 The native library ships prebuilt per platform (Linux, macOS, Windows — x64 and