fix(container-runner): raise install_packages build timeout to 15min

The 5-minute timeout in buildAgentGroupImage was tight for first-time
apt + pnpm global installs on slow networks (the exact scenario
install_packages triggers, since the image hasn't pre-installed the
requested packages). Hit ETIMEDOUT on a real install with apt + npm
packages.

900_000ms gives realistic headroom without masking genuinely hung builds.

src/container-runner.ts

@@ -530,7 +530,7 @@ export async function buildAgentGroupImage(agentGroupId: string): Promise<void>
     execSync(`${CONTAINER_RUNTIME_BIN} build -t ${imageTag} -f ${tmpDockerfile} .`, {
       cwd: DATA_DIR,
       stdio: 'pipe',
-      timeout: 300_000,
+      timeout: 900_000,
     });
   } finally {
     fs.unlinkSync(tmpDockerfile);