feat(storage): add ArtifactStore interface

cameleer-server-core/src/main/java/com/cameleer/server/core/storage/ArtifactStore.java

@@ -0,0 +1,35 @@
+package com.cameleer.server.core.storage;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * Storage abstraction for deployable JAR artifacts. Implementations decide where
+ * the bytes live (filesystem today; OCI registry / S3 later — see Zot follow-up
+ * issue #158). Callers never construct filesystem paths themselves.
+ *
+ * <p>The interface is intentionally narrow: enough to upload, fetch, and delete.
+ * {@link #locator} returns a stable identifier written into
+ * {@code app_versions.jar_path} so existing rows still resolve.
+ */
+public interface ArtifactStore {
+
+    /** Persist {@code bytes} of {@code size} bytes under {@code coords}. Idempotent
+     * on identical content; overwrites on same coords with different content.
+     * Returns the locator (same as {@link #locator}) for convenience. */
+    String put(ArtifactCoordinates coords, InputStream bytes, long size) throws IOException;
+
+    /** Open the artifact for reading. Caller closes. */
+    InputStream get(ArtifactCoordinates coords) throws IOException;
+
+    boolean exists(ArtifactCoordinates coords);
+
+    /** Remove the artifact and any backend-specific scaffolding (empty parent dirs, etc.).
+     * Silently no-ops if the artifact is already absent. */
+    void delete(ArtifactCoordinates coords) throws IOException;
+
+    /** Stable identifier for this storage location — written into
+     * {@code app_versions.jar_path} so existing rows still resolve. For the
+     * filesystem store this is the absolute path; for OCI it's the ref. */
+    String locator(ArtifactCoordinates coords);
+}