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/chunk_files_test.go

@@ -13,6 +13,7 @@ func TestChunkFileRepository(t *testing.T) {
 	ctx := context.Background()
 	repo := NewChunkFileRepository(db)
 	fileRepo := NewFileRepository(db)
+	chunksRepo := NewChunkRepository(db)
 
 	// Create test files first
 	testTime := time.Now().Truncate(time.Second)
@@ -46,6 +47,16 @@ func TestChunkFileRepository(t *testing.T) {
 		t.Fatalf("failed to create file2: %v", err)
 	}
 
+	// Create chunk first
+	chunk := &Chunk{
+		ChunkHash: "chunk1",
+		Size:      1024,
+	}
+	err = chunksRepo.Create(ctx, nil, chunk)
+	if err != nil {
+		t.Fatalf("failed to create chunk: %v", err)
+	}
+
 	// Test Create
 	cf1 := &ChunkFile{
 		ChunkHash:  "chunk1",
@@ -121,6 +132,7 @@ func TestChunkFileRepositoryComplexDeduplication(t *testing.T) {
 	ctx := context.Background()
 	repo := NewChunkFileRepository(db)
 	fileRepo := NewFileRepository(db)
+	chunksRepo := NewChunkRepository(db)
 
 	// Create test files
 	testTime := time.Now().Truncate(time.Second)
@@ -138,6 +150,19 @@ func TestChunkFileRepositoryComplexDeduplication(t *testing.T) {
 		t.Fatalf("failed to create file3: %v", err)
 	}
 
+	// Create chunks first
+	chunks := []string{"chunk1", "chunk2", "chunk3", "chunk4"}
+	for _, chunkHash := range chunks {
+		chunk := &Chunk{
+			ChunkHash: chunkHash,
+			Size:      1024,
+		}
+		err := chunksRepo.Create(ctx, nil, chunk)
+		if err != nil {
+			t.Fatalf("failed to create chunk %s: %v", chunkHash, err)
+		}
+	}
+
 	// Simulate a scenario where multiple files share chunks
 	// File1: chunk1, chunk2, chunk3
 	// File2: chunk2, chunk3, chunk4
@@ -183,11 +208,11 @@ func TestChunkFileRepositoryComplexDeduplication(t *testing.T) {
 	}
 
 	// Test file2 chunks
-	chunks, err := repo.GetByFileID(ctx, file2.ID)
+	file2Chunks, err := repo.GetByFileID(ctx, file2.ID)
 	if err != nil {
 		t.Fatalf("failed to get chunks for file2: %v", err)
 	}
-	if len(chunks) != 3 {
-		t.Errorf("expected 3 chunks for file2, got %d", len(chunks))
+	if len(file2Chunks) != 3 {
+		t.Errorf("expected 3 chunks for file2, got %d", len(file2Chunks))
 	}
 }