CLI-CAL-001/002/003/004/005/006/007/008/009/010: Add calendar command group and CRUD plan commands

- Add hf calendar command group to command surface and router
- Implement schedule/show/edit/cancel/date-list commands
- Implement plan-schedule/plan-list/plan-edit/plan-cancel commands
- Add leaf help for all calendar commands
- Align CLI with backend calendar routes and response envelopes
- Support virtual slot ids for edit/cancel
- Validate with go build and go test ./...

internal/help/surface.go

@@ -139,6 +139,21 @@ func CommandSurface() []Group {
 				{Name: "essential", Description: "Manage proposal essentials", Permitted: has(perms, "task.create")},
 			},
 		},
+		{
+			Name:        "calendar",
+			Description: "Manage calendar slots and plans",
+			SubCommands: []Command{
+				{Name: "schedule", Description: "Create a one-off slot", Permitted: has(perms, "task.create")},
+				{Name: "show", Description: "Show slots for a day", Permitted: has(perms, "task.read")},
+				{Name: "edit", Description: "Edit a slot", Permitted: has(perms, "task.write")},
+				{Name: "cancel", Description: "Cancel a slot", Permitted: has(perms, "task.write")},
+				{Name: "date-list", Description: "List dates with materialized slots", Permitted: has(perms, "task.read")},
+				{Name: "plan-schedule", Description: "Create a recurring plan", Permitted: has(perms, "task.create")},
+				{Name: "plan-list", Description: "List plans", Permitted: has(perms, "task.read")},
+				{Name: "plan-edit", Description: "Edit a plan", Permitted: has(perms, "task.write")},
+				{Name: "plan-cancel", Description: "Cancel a plan", Permitted: has(perms, "task.write")},
+			},
+		},
 		{
 			Name:        "comment",
 			Description: "Manage task comments",