proto: add public, ref_count, deduplicated, checksum filter fields for unified file storage

proto/database.proto

@@ -459,15 +459,17 @@ message FileMetadata {
     string name = 2;
     string mime_type = 3;
     uint64 size = 4;
-    string file_type = 5;             // audio/recording, pcap, upload
-    string related_id = 6;            // e.g., call_id for recordings
+    string file_type = 5;             // "plugin", "document", "generated"
+    string related_id = 6;            // plugin_id, conversation_id, etc.
     map<string, string> metadata = 7; // Custom metadata
+    bool is_public = 8;               // Visibility flag
 }
 
 message UploadFileResponse {
     string id = 1;
     uint64 size = 2;
     string checksum = 3;              // SHA-256
+    bool deduplicated = 4;            // True if blob already existed
 }
 
 message DownloadFileRequest {
@@ -496,6 +498,8 @@ message FileInfo {
     string checksum = 7;
     uint64 created_at = 8;
     map<string, string> metadata = 9;
+    bool is_public = 10;              // Visibility flag
+    uint32 ref_count = 11;            // Blob reference count (informational)
 }
 
 message ListFilesRequest {
@@ -503,6 +507,7 @@ message ListFilesRequest {
     string related_id = 2;            // Filter by related ID (optional)
     uint32 limit = 3;
     uint32 offset = 4;
+    string checksum = 5;             // Filter by checksum (for dedup queries)
 }
 
 message ListFilesResponse {