feat(node-sdk): expose subagent task query API

[ZhiXiao-Lin]

Stacked on #36 (which is stacked on #35). When the upstream PRs land the base of this PR will retarget to `main` automatically.

Summary

Mirrors the core-side subagent query API (#35) onto the Node SDK so JS/TS callers don't have to parse the raw event stream.

```ts
const snap = await session.subagentTask('task-abc')
// { taskId, parentSessionId, childSessionId, agent, description,
// status: 'running' | 'completed' | 'failed',
// startedMs, updatedMs, finishedMs?, output?, success?, progress: [...] }

const all = await session.subagentTasks()
const pending = await session.pendingSubagentTasks()
```

Notes on the regenerated `index.d.ts`

The file is `auto-generated by NAPI-RS` per its header. Building picked up:

• The three new methods.
• Docstring drift — several `errorKindJson` comments in the previous .d.ts were richer than the current Rust source; napi regenerated them to match the Rust truth. No semantic change.
• Reordering of generated interfaces (e.g. `AutoDelegationOptions` moved earlier in the file). Every `export` declaration from the previous file is still present (verified with a sorted-export diff).

The hand-added type aliases that aren't generated from Rust — `ToolErrorKind`, `VerificationStatus`, `VerificationCheck`, `VerificationReport`, `ToolArtifact` — were lost by the regeneration and restored as part of this commit. They probably belong in a separate non-generated `index.types.ts` long-term, but that's out of scope here.

Test plan

• `npm run build:debug` succeeds.
• `npm test` passes, including the new smoke block:
  • `subagentTasks()` returns `[]` for a fresh session
  • `pendingSubagentTasks()` returns `[]` for a fresh session
  • `subagentTask('task-does-not-exist')` returns `null`
• Sorted-export diff confirms no exported symbols were dropped.

Follow-ups

• PR Orchestrator does not execute custom agent definitions from agent_dirs #4: Python SDK alignment (also needs the missing `runs/run_events` family).
• PR Orchestrator API: sub-agent event streaming and fine-grained permissive control #5: cancellation by task id.