fix: Throw exception on bucket creation failure in S3VolumeManager

Fixes #210

Changed ensureBucketExists() to throw RuntimeException when bucket creation
or verification fails, instead of silently swallowing the exception. This
prevents S3VolumeManager from entering an initialized state when the bucket
doesn't actually exist.

Changes:
- Throw RuntimeException when createBucket() fails
- Throw RuntimeException when headBucket() fails (outer catch)
- Add success log message after bucket creation
- Include clear error messages about credentials and permissions
- Wrap original exception as cause for debugging

Before this fix, start() would set initialized=true even when bucket
creation failed, leaving the manager in a broken state where all subsequent
operations would fail with confusing errors.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Flossy

jplatform-storage-s3/src/main/java/org/flossware/jplatform/storage/s3/S3VolumeManager.java

@@ -308,9 +308,15 @@ private void ensureBucketExists() {
                 s3Client.createBucket(CreateBucketRequest.builder()
                     .bucket(config.getBucketName())
                     .build());
+                logger.info("Successfully created bucket: {}", config.getBucketName());
             } catch (Exception ex) {
                 logger.error("Failed to create bucket: " + config.getBucketName(), ex);
+                throw new RuntimeException("Failed to create S3 bucket: " + config.getBucketName() +
+                    ". Check credentials and permissions.", ex);
             }
+        } catch (Exception e) {
+            logger.error("Failed to verify bucket existence: " + config.getBucketName(), e);
+            throw new RuntimeException("Failed to verify S3 bucket: " + config.getBucketName(), e);
         }
     }