Implement SQLite index database layer

- Add pure Go SQLite driver (modernc.org/sqlite) to avoid CGO dependency
- Implement database connection management with WAL mode
- Add write mutex for serializing concurrent writes
- Create schema for all tables matching DESIGN.md specifications
- Implement repository pattern for all database entities:
  - Files, FileChunks, Chunks, Blobs, BlobChunks, ChunkFiles, Snapshots
- Add transaction support with proper rollback handling
- Add fatal error handling for database integrity issues
- Add snapshot fields for tracking file sizes and compression ratios
- Make index path configurable via VAULTIK_INDEX_PATH environment variable
- Add comprehensive test coverage for all repositories
- Add format check to Makefile to ensure code formatting

internal/database/blobs_test.go

@@ -0,0 +1,100 @@
+package database
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestBlobRepository(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewBlobRepository(db)
+
+	// Test Create
+	blob := &Blob{
+		BlobHash:  "blobhash123",
+		CreatedTS: time.Now().Truncate(time.Second),
+	}
+
+	err := repo.Create(ctx, nil, blob)
+	if err != nil {
+		t.Fatalf("failed to create blob: %v", err)
+	}
+
+	// Test GetByHash
+	retrieved, err := repo.GetByHash(ctx, blob.BlobHash)
+	if err != nil {
+		t.Fatalf("failed to get blob: %v", err)
+	}
+	if retrieved == nil {
+		t.Fatal("expected blob, got nil")
+	}
+	if retrieved.BlobHash != blob.BlobHash {
+		t.Errorf("blob hash mismatch: got %s, want %s", retrieved.BlobHash, blob.BlobHash)
+	}
+	if !retrieved.CreatedTS.Equal(blob.CreatedTS) {
+		t.Errorf("created timestamp mismatch: got %v, want %v", retrieved.CreatedTS, blob.CreatedTS)
+	}
+
+	// Test List
+	blob2 := &Blob{
+		BlobHash:  "blobhash456",
+		CreatedTS: time.Now().Truncate(time.Second),
+	}
+	err = repo.Create(ctx, nil, blob2)
+	if err != nil {
+		t.Fatalf("failed to create second blob: %v", err)
+	}
+
+	blobs, err := repo.List(ctx, 10, 0)
+	if err != nil {
+		t.Fatalf("failed to list blobs: %v", err)
+	}
+	if len(blobs) != 2 {
+		t.Errorf("expected 2 blobs, got %d", len(blobs))
+	}
+
+	// Test pagination
+	blobs, err = repo.List(ctx, 1, 0)
+	if err != nil {
+		t.Fatalf("failed to list blobs with limit: %v", err)
+	}
+	if len(blobs) != 1 {
+		t.Errorf("expected 1 blob with limit, got %d", len(blobs))
+	}
+
+	blobs, err = repo.List(ctx, 1, 1)
+	if err != nil {
+		t.Fatalf("failed to list blobs with offset: %v", err)
+	}
+	if len(blobs) != 1 {
+		t.Errorf("expected 1 blob with offset, got %d", len(blobs))
+	}
+}
+
+func TestBlobRepositoryDuplicate(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewBlobRepository(db)
+
+	blob := &Blob{
+		BlobHash:  "duplicate_blob",
+		CreatedTS: time.Now().Truncate(time.Second),
+	}
+
+	err := repo.Create(ctx, nil, blob)
+	if err != nil {
+		t.Fatalf("failed to create blob: %v", err)
+	}
+
+	// Try to create duplicate - should fail due to unique constraint
+	err = repo.Create(ctx, nil, blob)
+	if err == nil {
+		t.Error("expected error for duplicate blob")
+	}
+}