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/file_chunks_test.go

@@ -0,0 +1,119 @@
+package database
+
+import (
+	"context"
+	"fmt"
+	"testing"
+)
+
+func TestFileChunkRepository(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewFileChunkRepository(db)
+
+	// Test Create
+	fc1 := &FileChunk{
+		Path:      "/test/file.txt",
+		Idx:       0,
+		ChunkHash: "chunk1",
+	}
+
+	err := repo.Create(ctx, nil, fc1)
+	if err != nil {
+		t.Fatalf("failed to create file chunk: %v", err)
+	}
+
+	// Add more chunks for the same file
+	fc2 := &FileChunk{
+		Path:      "/test/file.txt",
+		Idx:       1,
+		ChunkHash: "chunk2",
+	}
+	err = repo.Create(ctx, nil, fc2)
+	if err != nil {
+		t.Fatalf("failed to create second file chunk: %v", err)
+	}
+
+	fc3 := &FileChunk{
+		Path:      "/test/file.txt",
+		Idx:       2,
+		ChunkHash: "chunk3",
+	}
+	err = repo.Create(ctx, nil, fc3)
+	if err != nil {
+		t.Fatalf("failed to create third file chunk: %v", err)
+	}
+
+	// Test GetByPath
+	chunks, err := repo.GetByPath(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))
+	}
+
+	// Verify order
+	for i, chunk := range chunks {
+		if chunk.Idx != i {
+			t.Errorf("wrong chunk order: expected idx %d, got %d", i, chunk.Idx)
+		}
+	}
+
+	// Test duplicate insert (should be idempotent)
+	err = repo.Create(ctx, nil, fc1)
+	if err != nil {
+		t.Fatalf("failed to create duplicate file chunk: %v", err)
+	}
+
+	// Test DeleteByPath
+	err = repo.DeleteByPath(ctx, nil, "/test/file.txt")
+	if err != nil {
+		t.Fatalf("failed to delete file chunks: %v", err)
+	}
+
+	chunks, err = repo.GetByPath(ctx, "/test/file.txt")
+	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))
+	}
+}
+
+func TestFileChunkRepositoryMultipleFiles(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewFileChunkRepository(db)
+
+	// Create chunks for multiple files
+	files := []string{"/file1.txt", "/file2.txt", "/file3.txt"}
+	for _, path := range files {
+		for i := 0; i < 2; i++ {
+			fc := &FileChunk{
+				Path:      path,
+				Idx:       i,
+				ChunkHash: fmt.Sprintf("%s_chunk%d", path, i),
+			}
+			err := repo.Create(ctx, nil, fc)
+			if err != nil {
+				t.Fatalf("failed to create file chunk: %v", err)
+			}
+		}
+	}
+
+	// Verify each file has correct chunks
+	for _, path := range files {
+		chunks, err := repo.GetByPath(ctx, path)
+		if err != nil {
+			t.Fatalf("failed to get chunks for %s: %v", path, err)
+		}
+		if len(chunks) != 2 {
+			t.Errorf("expected 2 chunks for %s, got %d", path, len(chunks))
+		}
+	}
+}