feat: external-cancel polling via heartbeat-runs endpoint (FAR-42)

Poll PAPERCLIP_API_URL/api/heartbeat-runs/{runId} at keepalive cadence
during log streaming. When status != "running", delete the Job with
propagationPolicy=Background and return errorCode="cancelled" as a
distinct result, matching the claude_k8s reference implementation.

Also includes: reattachOrphanedJobs config field that lets the adapter
reattach to a same-task Job left over from a prior server restart;
task-id and session-id K8s labels on Job manifests for observability.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/job-manifest.ts

@@ -320,6 +320,9 @@ export function buildJobManifest(input: JobBuildInput): JobBuildResult {
     "paperclip.io/company-id": sanitizeLabelValue(agent.companyId, warnLabel),
     "paperclip.io/adapter-type": "opencode_k8s",
   };
+  const taskId = asString(context.taskId ?? context.issueId, "").trim();
+  if (taskId) labels["paperclip.io/task-id"] = sanitizeLabelValue(taskId, warnLabel);
+  if (runtimeSessionId) labels["paperclip.io/session-id"] = sanitizeLabelValue(runtimeSessionId, warnLabel);
   for (const [key, value] of Object.entries(extraLabels)) {
     if (typeof value === "string") labels[key] = sanitizeLabelValue(value, warnLabel);
   }