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/examples/agent-spine-demo/tests/agent-core.spec.ts

@@ -9,6 +9,12 @@ import * as agentCore from '../src/index.ts'
 import { AgentId, agentEvents, type Agent } from '@deepseek-ai/dsh-agent'
 import { CallId, type Message } from '@deepseek-ai/dsh-llm'
 
+declare module '@deepseek-ai/dsh-tasks' {
+  interface TaskKindMap {
+    probe: 'probe'
+  }
+}
+
 async function composePrefix(ctx: Context, cwd: string): Promise<Message[]> {
   const agent = { session: { header: { cwd } } } as unknown as Agent
   const empty: Message[] = []