fix(tasks): address task API review feedback

The public kill result used the awkward phrase already-terminal. Rename it to already-finished and keep the model-facing response aligned; not-alive would be inaccurate because a force-failed registry record can still correspond to orphaned producer work.

Task kinds were open strings even though producer namespaces are an extension point. Add the merge-extensible TaskKindMap and derived TaskKind, cover consumer declarations in task and bundle tests, and retain the runtime non-empty check for untyped callers.

With exactOptionalPropertyTypes, owner?: Agent | undefined allowed an explicit undefined value that no caller needs. Tighten the property to owner?: Agent so unowned work is expressed by omitting it.

Record the requested task-service/backend split as a follow-up, using a systemd-backed runtime as a concrete candidate without guessing its durability and ownership contract in this PR. Regenerate the type and Cordis catalogs so public docs match the declarations.

packages/tasks/tool-tasks/src/index.ts

@@ -136,7 +136,7 @@ export function apply(ctx: Context, config: Config): void {
     execute(args, exec) {
       const id = validateTaskId(args.task_id)
       const result = ctx.tasks.kill(id, exec.agent, args.reason)
-      if (result === 'already-terminal') {
+      if (result === 'already-finished') {
         // A snapshot describes terminal state without consuming pending output.
         const snapshot = ctx.tasks.get(id, exec.agent)
         return Promise.resolve([{ type: 'text', text: `task ${id} had already finished ${statusLine(snapshot)}` }])