feat(v0.3): add --project flag, CTASK_TYPE env, project root semantics

ctask new gains --project, which:
  - records type=project on the workspace
  - defaults the category to "projects"
  - applies general + project seed overlays
  - uses CTASK_PROJECT_ROOT when set, with no doubled "projects/"
    path unless the user explicitly passes -c
  - exports CTASK_TYPE=project into the child session

EnvVars now takes a taskType arg and exports CTASK_TYPE. Empty
type defaults to "task" for safety. resume/open also pass
EffectiveType so the env var is correct on resume of a v0.2
workspace.

Git init for project mode is wired in the next commit.

internal/config/config.go

@@ -60,13 +60,18 @@ func ResolveProjectRoot() string {
 }
 
 // EnvVars returns the environment variables to export into child sessions.
-func EnvVars(slug, mode, root, workspace, category string) map[string]string {
+// taskType must be "task" or "project"; an empty value defaults to "task".
+func EnvVars(slug, mode, root, workspace, category, taskType string) map[string]string {
+	if taskType == "" {
+		taskType = "task"
+	}
 	return map[string]string{
 		"CTASK_TASK":      slug,
 		"CTASK_MODE":      mode,
 		"CTASK_ROOT":      root,
 		"CTASK_WORKSPACE": workspace,
 		"CTASK_CATEGORY":  category,
+		"CTASK_TYPE":      taskType,
 	}
 }
 

internal/config/config_test.go

@@ -145,13 +145,14 @@ func TestResolveProjectRootOverride(t *testing.T) {
 }
 
 func TestEnvVars(t *testing.T) {
-	vars := EnvVars("my-slug", "local", "/abs/root", "/abs/root/cat/ws", "general")
+	vars := EnvVars("my-slug", "local", "/abs/root", "/abs/root/cat/ws", "general", "task")
 	expected := map[string]string{
 		"CTASK_TASK":      "my-slug",
 		"CTASK_MODE":      "local",
 		"CTASK_ROOT":      "/abs/root",
 		"CTASK_WORKSPACE": "/abs/root/cat/ws",
 		"CTASK_CATEGORY":  "general",
+		"CTASK_TYPE":      "task",
 	}
 	for k, v := range expected {
 		if vars[k] != v {
@@ -159,3 +160,17 @@ func TestEnvVars(t *testing.T) {
 		}
 	}
 }
+
+func TestEnvVarsProjectType(t *testing.T) {
+	vars := EnvVars("p", "local", "/r", "/r/p", "projects", "project")
+	if vars["CTASK_TYPE"] != "project" {
+		t.Errorf("CTASK_TYPE: got %q, want \"project\"", vars["CTASK_TYPE"])
+	}
+}
+
+func TestEnvVarsEmptyTypeDefaultsToTask(t *testing.T) {
+	vars := EnvVars("p", "local", "/r", "/r/p", "general", "")
+	if vars["CTASK_TYPE"] != "task" {
+		t.Errorf("CTASK_TYPE empty fallback: got %q, want \"task\"", vars["CTASK_TYPE"])
+	}
+}