Fix foreign key constraints and improve snapshot tracking

- Add unified compression/encryption package in internal/blobgen
- Update DATAMODEL.md to reflect current schema implementation
- Refactor snapshot cleanup into well-named methods for clarity
- Add snapshot_id to uploads table to track new blobs per snapshot
- Fix blob count reporting for incremental backups
- Add DeleteOrphaned method to BlobChunkRepository
- Fix cleanup order to respect foreign key constraints
- Update tests to reflect schema changes

internal/database/file_chunks_test.go

@@ -32,6 +32,20 @@ func TestFileChunkRepository(t *testing.T) {
 		t.Fatalf("failed to create file: %v", err)
 	}
 
+	// Create chunks first
+	chunks := []string{"chunk1", "chunk2", "chunk3"}
+	chunkRepo := NewChunkRepository(db)
+	for _, chunkHash := range chunks {
+		chunk := &Chunk{
+			ChunkHash: chunkHash,
+			Size:      1024,
+		}
+		err = chunkRepo.Create(ctx, nil, chunk)
+		if err != nil {
+			t.Fatalf("failed to create chunk %s: %v", chunkHash, err)
+		}
+	}
+
 	// Test Create
 	fc1 := &FileChunk{
 		FileID:    file.ID,
@@ -66,16 +80,16 @@ func TestFileChunkRepository(t *testing.T) {
 	}
 
 	// Test GetByFile
-	chunks, err := repo.GetByFile(ctx, "/test/file.txt")
+	fileChunks, err := repo.GetByFile(ctx, "/test/file.txt")
 	if err != nil {
 		t.Fatalf("failed to get file chunks: %v", err)
 	}
-	if len(chunks) != 3 {
-		t.Errorf("expected 3 chunks, got %d", len(chunks))
+	if len(fileChunks) != 3 {
+		t.Errorf("expected 3 chunks, got %d", len(fileChunks))
 	}
 
 	// Verify order
-	for i, chunk := range chunks {
+	for i, chunk := range fileChunks {
 		if chunk.Idx != i {
 			t.Errorf("wrong chunk order: expected idx %d, got %d", i, chunk.Idx)
 		}
@@ -93,12 +107,12 @@ func TestFileChunkRepository(t *testing.T) {
 		t.Fatalf("failed to delete file chunks: %v", err)
 	}
 
-	chunks, err = repo.GetByFileID(ctx, file.ID)
+	fileChunks, err = repo.GetByFileID(ctx, file.ID)
 	if err != nil {
 		t.Fatalf("failed to get deleted file chunks: %v", err)
 	}
-	if len(chunks) != 0 {
-		t.Errorf("expected 0 chunks after delete, got %d", len(chunks))
+	if len(fileChunks) != 0 {
+		t.Errorf("expected 0 chunks after delete, got %d", len(fileChunks))
 	}
 }
 
@@ -133,6 +147,22 @@ func TestFileChunkRepositoryMultipleFiles(t *testing.T) {
 		files[i] = file
 	}
 
+	// Create all chunks first
+	chunkRepo := NewChunkRepository(db)
+	for i := range files {
+		for j := 0; j < 2; j++ {
+			chunkHash := fmt.Sprintf("file%d_chunk%d", i, j)
+			chunk := &Chunk{
+				ChunkHash: chunkHash,
+				Size:      1024,
+			}
+			err := chunkRepo.Create(ctx, nil, chunk)
+			if err != nil {
+				t.Fatalf("failed to create chunk %s: %v", chunkHash, err)
+			}
+		}
+	}
+
 	// Create chunks for multiple files
 	for i, file := range files {
 		for j := 0; j < 2; j++ {