build(java): resolve Lance preview dependencies from R2 (#4476)

Lance beta and RC artifacts are moving to `https://maven.lance.org`. Add
that release repository to the Java parent POM so LanceDB can resolve
explicit preview versions from it, while keeping Maven Central available
for historical releases and other dependencies.

Validated resolution of `org.lance:lance-core:14.0.0-beta.3` from a
fresh Maven cache using the actual `lancedb-core` POM. Maven recorded
the new `lance` repository as the source of both the POM and JAR. The
pinned Lance version and LanceDB's own publishing workflow are
unchanged.

java/README.md

@@ -73,6 +73,11 @@ reader usually expects:
 
 ## Development
 
+The parent POM includes `https://maven.lance.org` to resolve Lance beta and RC
+dependencies. Use an explicit `lance-core.version`; numbered beta and RC versions
+are Maven releases, not snapshots. Maven Central remains available for stable
+and historical versions, as well as other dependencies.
+
 Build:
 
 ```shell

java/pom.xml

@@ -95,6 +95,16 @@
         </dependencies>
     </dependencyManagement>
 
+    <repositories>
+        <repository>
+            <id>lance</id>
+            <url>https://maven.lance.org</url>
+            <snapshots>
+                <enabled>false</enabled>
+            </snapshots>
+        </repository>
+    </repositories>
+
     <distributionManagement>
         <snapshotRepository>
             <id>ossrh</id>