CLI-PR-001/002/003/004: Rename propose->proposal, add essential commands, improve accept, restrict story

- Rename 'propose' group to 'proposal' in surface, leaf help, and routing
- Keep 'hf propose' as backward-compatible alias via groupAliases
- Add essential subcommand group: list, create, update, delete
- Accept command now shows generated story tasks in output
- Accept command supports --json output
- Task create blocks story/* types with helpful error message
- All help text updated to use 'proposal' terminology

internal/help/surface.go

@@ -126,16 +126,17 @@ func CommandSurface() []Group {
 			},
 		},
 		{
-			Name:        "propose",
+			Name:        "proposal",
 			Description: "Manage proposals",
 			SubCommands: []Command{
 				{Name: "list", Description: "List proposals", Permitted: has(perms, "project.read")},
 				{Name: "get", Description: "Show a proposal by code", Permitted: has(perms, "project.read")},
 				{Name: "create", Description: "Create a proposal", Permitted: has(perms, "task.create")},
 				{Name: "update", Description: "Update a proposal", Permitted: has(perms, "task.write")},
-				{Name: "accept", Description: "Accept a proposal", Permitted: has(perms, "propose.accept")},
+				{Name: "accept", Description: "Accept a proposal and generate story tasks", Permitted: has(perms, "propose.accept")},
 				{Name: "reject", Description: "Reject a proposal", Permitted: has(perms, "propose.reject")},
 				{Name: "reopen", Description: "Reopen a proposal", Permitted: has(perms, "propose.reopen")},
+				{Name: "essential", Description: "Manage proposal essentials", Permitted: has(perms, "task.create")},
 			},
 		},
 		{