release: bump 0.8.8 -> 0.8.9 (#285)

Maintenance release — supply-chain and CI housekeeping only. No library code or
public API changes.

### Security
- Triaged the pyo3 advisories RUSTSEC-2026-0176 / RUSTSEC-2026-0177 as not
  affecting Wickra (vulnerable APIs unreachable from the binding; fix blocked
  upstream by rust-numpy pinning pyo3 `^0.28`). Recorded in `deny.toml` and
  `osv-scanner.toml`.

### Changed
- Java binding: `central-publishing-maven-plugin` 0.5.0 → 0.10.0.
- CI GitHub Actions bumped to latest (checkout, setup-go, setup-java,
  codeql-action, taiki-e/install-action).
- Added a Maven ecosystem to Dependabot.

Version bumped across all manifests/lockfiles via `bump_version.py`; Cargo.lock
refreshed. CHANGELOG `[0.8.9]` filled. Tag/publish to follow on explicit GO.

examples/java/pom.xml

@@ -6,7 +6,7 @@
 
   <groupId>org.wickra.examples</groupId>
   <artifactId>wickra-examples</artifactId>
-  <version>0.8.8</version>
+  <version>0.8.9</version>
   <packaging>jar</packaging>
 
   <name>Wickra Java examples</name>
@@ -21,7 +21,7 @@
     <dependency>
       <groupId>org.wickra</groupId>
       <artifactId>wickra</artifactId>
-      <version>0.8.8</version>
+      <version>0.8.9</version>
     </dependency>
     <!-- Only the network examples (fetch_btcusdt) parse JSON. -->
     <dependency>