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/chunks_test.go

@@ -0,0 +1,104 @@
+package database
+
+import (
+	"context"
+	"testing"
+)
+
+func TestChunkRepository(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewChunkRepository(db)
+
+	// Test Create
+	chunk := &Chunk{
+		ChunkHash: "chunkhash123",
+		SHA256:    "sha256hash123",
+		Size:      4096,
+	}
+
+	err := repo.Create(ctx, nil, chunk)
+	if err != nil {
+		t.Fatalf("failed to create chunk: %v", err)
+	}
+
+	// Test GetByHash
+	retrieved, err := repo.GetByHash(ctx, chunk.ChunkHash)
+	if err != nil {
+		t.Fatalf("failed to get chunk: %v", err)
+	}
+	if retrieved == nil {
+		t.Fatal("expected chunk, got nil")
+	}
+	if retrieved.ChunkHash != chunk.ChunkHash {
+		t.Errorf("chunk hash mismatch: got %s, want %s", retrieved.ChunkHash, chunk.ChunkHash)
+	}
+	if retrieved.SHA256 != chunk.SHA256 {
+		t.Errorf("sha256 mismatch: got %s, want %s", retrieved.SHA256, chunk.SHA256)
+	}
+	if retrieved.Size != chunk.Size {
+		t.Errorf("size mismatch: got %d, want %d", retrieved.Size, chunk.Size)
+	}
+
+	// Test duplicate insert (should be idempotent)
+	err = repo.Create(ctx, nil, chunk)
+	if err != nil {
+		t.Fatalf("failed to create duplicate chunk: %v", err)
+	}
+
+	// Test GetByHashes
+	chunk2 := &Chunk{
+		ChunkHash: "chunkhash456",
+		SHA256:    "sha256hash456",
+		Size:      8192,
+	}
+	err = repo.Create(ctx, nil, chunk2)
+	if err != nil {
+		t.Fatalf("failed to create second chunk: %v", err)
+	}
+
+	chunks, err := repo.GetByHashes(ctx, []string{chunk.ChunkHash, chunk2.ChunkHash})
+	if err != nil {
+		t.Fatalf("failed to get chunks by hashes: %v", err)
+	}
+	if len(chunks) != 2 {
+		t.Errorf("expected 2 chunks, got %d", len(chunks))
+	}
+
+	// Test ListUnpacked
+	unpacked, err := repo.ListUnpacked(ctx, 10)
+	if err != nil {
+		t.Fatalf("failed to list unpacked chunks: %v", err)
+	}
+	if len(unpacked) != 2 {
+		t.Errorf("expected 2 unpacked chunks, got %d", len(unpacked))
+	}
+}
+
+func TestChunkRepositoryNotFound(t *testing.T) {
+	db, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+	repo := NewChunkRepository(db)
+
+	// Test GetByHash with non-existent hash
+	chunk, err := repo.GetByHash(ctx, "nonexistent")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if chunk != nil {
+		t.Error("expected nil for non-existent chunk")
+	}
+
+	// Test GetByHashes with empty list
+	chunks, err := repo.GetByHashes(ctx, []string{})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if chunks != nil {
+		t.Error("expected nil for empty hash list")
+	}
+}