feat(store): add blob, file, folder, and upload stores

Add BlobStore (ref counting), FileStore (soft delete + pagination), FolderStore (materialized path), UploadStore (idempotent upsert), and update AutoMigrate.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/store/blob_store_test.go

@@ -0,0 +1,146 @@
+package store
+
+import (
+	"context"
+	"testing"
+
+	"gcy_hpc_server/internal/model"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+func setupBlobTestDB(t *testing.T) *gorm.DB {
+	t.Helper()
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.FileBlob{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	return db
+}
+
+func TestBlobStore_Create(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	blob := &model.FileBlob{
+		SHA256:   "abc123",
+		MinioKey: "files/abc123",
+		FileSize: 1024,
+		MimeType: "application/octet-stream",
+		RefCount: 0,
+	}
+	if err := store.Create(ctx, blob); err != nil {
+		t.Fatalf("Create() error = %v", err)
+	}
+	if blob.ID == 0 {
+		t.Error("Create() did not set ID")
+	}
+}
+
+func TestBlobStore_GetBySHA256(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	store.Create(ctx, &model.FileBlob{SHA256: "abc", MinioKey: "files/abc", FileSize: 100, RefCount: 0})
+
+	blob, err := store.GetBySHA256(ctx, "abc")
+	if err != nil {
+		t.Fatalf("GetBySHA256() error = %v", err)
+	}
+	if blob == nil {
+		t.Fatal("GetBySHA256() returned nil")
+	}
+	if blob.SHA256 != "abc" {
+		t.Errorf("SHA256 = %q, want %q", blob.SHA256, "abc")
+	}
+	if blob.RefCount != 0 {
+		t.Errorf("RefCount = %d, want 0", blob.RefCount)
+	}
+}
+
+func TestBlobStore_GetBySHA256_NotFound(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	blob, err := store.GetBySHA256(ctx, "nonexistent")
+	if err != nil {
+		t.Fatalf("GetBySHA256() error = %v", err)
+	}
+	if blob != nil {
+		t.Error("GetBySHA256() should return nil for not found")
+	}
+}
+
+func TestBlobStore_IncrementDecrementRef(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	store.Create(ctx, &model.FileBlob{SHA256: "abc", MinioKey: "files/abc", FileSize: 100, RefCount: 0})
+
+	if err := store.IncrementRef(ctx, "abc"); err != nil {
+		t.Fatalf("IncrementRef() error = %v", err)
+	}
+	blob, _ := store.GetBySHA256(ctx, "abc")
+	if blob.RefCount != 1 {
+		t.Errorf("RefCount after 1st increment = %d, want 1", blob.RefCount)
+	}
+
+	store.IncrementRef(ctx, "abc")
+	blob, _ = store.GetBySHA256(ctx, "abc")
+	if blob.RefCount != 2 {
+		t.Errorf("RefCount after 2nd increment = %d, want 2", blob.RefCount)
+	}
+
+	refCount, err := store.DecrementRef(ctx, "abc")
+	if err != nil {
+		t.Fatalf("DecrementRef() error = %v", err)
+	}
+	if refCount != 1 {
+		t.Errorf("DecrementRef() returned %d, want 1", refCount)
+	}
+
+	refCount, _ = store.DecrementRef(ctx, "abc")
+	if refCount != 0 {
+		t.Errorf("DecrementRef() returned %d, want 0", refCount)
+	}
+}
+
+func TestBlobStore_Delete(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	store.Create(ctx, &model.FileBlob{SHA256: "abc", MinioKey: "files/abc", FileSize: 100, RefCount: 0})
+
+	if err := store.Delete(ctx, "abc"); err != nil {
+		t.Fatalf("Delete() error = %v", err)
+	}
+
+	blob, _ := store.GetBySHA256(ctx, "abc")
+	if blob != nil {
+		t.Error("Delete() did not remove blob")
+	}
+}
+
+func TestBlobStore_SHA256_UniqueConstraint(t *testing.T) {
+	db := setupBlobTestDB(t)
+	store := NewBlobStore(db)
+	ctx := context.Background()
+
+	store.Create(ctx, &model.FileBlob{SHA256: "dup", MinioKey: "files/dup1", FileSize: 100})
+	err := store.Create(ctx, &model.FileBlob{SHA256: "dup", MinioKey: "files/dup2", FileSize: 200})
+	if err == nil {
+		t.Error("expected error for duplicate SHA256, got nil")
+	}
+}