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.

examples/java/pom.xml

@@ -6,7 +6,7 @@
 
   <groupId>org.wickra.examples</groupId>
   <artifactId>wickra-examples</artifactId>
-  <version>0.8.5</version>
+  <version>0.8.6</version>
   <packaging>jar</packaging>
 
   <name>Wickra Java examples</name>
@@ -21,7 +21,7 @@
     <dependency>
       <groupId>org.wickra</groupId>
       <artifactId>wickra</artifactId>
-      <version>0.8.5</version>
+      <version>0.8.6</version>
     </dependency>
     <!-- Only the network examples (fetch_btcusdt) parse JSON. -->
     <dependency>