refactor: remove PAPERCLIP_DEV_API_KEY runtime hack throughout

Cancel poll now uses ctx.authToken exclusively. Remove forwarding of
PAPERCLIP_DEV_API_KEY into job pods and all associated tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/server/execute.ts

@@ -569,9 +569,7 @@ async function streamAndAwaitJob(
         await new Promise<void>((resolve) => setTimeout(resolve, KEEPALIVE_INTERVAL_MS));
         if (logStopSignal.stopped || cancelSignal.cancelled) break;
         try {
-          // Prefer PAPERCLIP_DEV_API_KEY if set (dev override), otherwise use
-          // the per-run authToken issued by Paperclip for this execution.
-          const apiKey = process.env.PAPERCLIP_DEV_API_KEY ?? ctx.authToken ?? "";
+          const apiKey = ctx.authToken ?? "";
           const resp = await fetch(`${apiUrl}/api/issues/${issueId}`, {
             headers: { Authorization: `Bearer ${apiKey}` },
           });