feat(v0.3): add SkipCategoryDir for CTASK_PROJECT_ROOT semantics

When SkipCategoryDir is true, Create places the workspace directly
under Root and does not append a Category subdirectory. This is the
mechanism that prevents doubled paths like
~/projects/projects/<slug> when the user sets CTASK_PROJECT_ROOT
without an explicit -c flag. The Category value is still recorded
on TaskMeta so list/info/filter still work.

internal/workspace/create.go

@@ -29,6 +29,12 @@ type CreateOpts struct {
 	// ProjectSeedDir is the absolute path to the project-specific seed directory.
 	// Only consulted when IsProject is true.
 	ProjectSeedDir string
+
+	// SkipCategoryDir, when true, places the workspace directly under Root
+	// without inserting a Category subdirectory. Used for project mode with
+	// CTASK_PROJECT_ROOT set and no explicit -c flag. Category is still
+	// recorded in TaskMeta.
+	SkipCategoryDir bool
 }
 
 // CreateResult holds the result of workspace creation.
@@ -60,7 +66,10 @@ func Create(opts CreateOpts) (*CreateResult, error) {
 	date := now.Format("2006-01-02")
 	id := now.Format("20060102-150405")
 
-	categoryDir := filepath.Join(opts.Root, opts.Category)
+	categoryDir := opts.Root
+	if !opts.SkipCategoryDir {
+		categoryDir = filepath.Join(opts.Root, opts.Category)
+	}
 	if err := os.MkdirAll(categoryDir, 0755); err != nil {
 		return nil, fmt.Errorf("creating category dir: %w", err)
 	}

internal/workspace/create_test.go

@@ -241,6 +241,51 @@ func TestCreateSeedDoesNotReplaceTaskYAML(t *testing.T) {
 	}
 }
 
+func TestCreateSkipCategoryDirPlacesUnderRoot(t *testing.T) {
+	root := t.TempDir()
+	opts := CreateOpts{
+		Root:            root,
+		Title:           "billing service",
+		Category:        "projects", // recorded in metadata
+		Mode:            "local",
+		Agent:           "claude",
+		IsProject:       true,
+		SkipCategoryDir: true,
+	}
+	ws, err := Create(opts)
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+	parent := filepath.Dir(ws.Path)
+	if parent != root {
+		t.Errorf("workspace parent: got %q, want %q", parent, root)
+	}
+	if ws.Meta.Category != "projects" {
+		t.Errorf("Category metadata: got %q, want \"projects\"", ws.Meta.Category)
+	}
+}
+
+func TestCreateExplicitCategoryAppendsSubdir(t *testing.T) {
+	root := t.TempDir()
+	opts := CreateOpts{
+		Root:      root,
+		Title:     "billing service",
+		Category:  "backend",
+		Mode:      "local",
+		Agent:     "claude",
+		IsProject: true,
+		// SkipCategoryDir: false (default)
+	}
+	ws, err := Create(opts)
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+	parent := filepath.Dir(ws.Path)
+	if parent != filepath.Join(root, "backend") {
+		t.Errorf("workspace parent: got %q, want %q", parent, filepath.Join(root, "backend"))
+	}
+}
+
 func TestCreateCollisionSuffix(t *testing.T) {
 	root := t.TempDir()