feat(webhooks): configurable agent run timeout (default 600s) (#1267)

Replace the hardcoded 30s webhook agent-run deadline with a configurable
timeout (default 600s, cap 3600s) for both the async worker and the
sync/test HTTP handler. Legitimate multi-step runs were dying at 30s
mid-tool-call; the same request over WebSocket completed fine.

- internal/webhooks/timeout.go: ResolveTimeoutSec helper (<=0 → 600s, cap 3600s)
- WorkerConfig.AsyncAgentTimeout (async worker) + WebhookLLMHandler.syncTimeout
  (sync + admin test), wired from config
- config keys gateway.webhook_{async,sync}_timeout_sec, also settable via
  GOCLAW_WEBHOOK_{ASYNC,SYNC}_TIMEOUT_SEC env (env overrides config)
- tests: timeout bounds + config file/env override

internal/webhooks/timeout.go

@@ -0,0 +1,24 @@
+package webhooks
+
+import "time"
+
+const (
+	// DefaultAgentTimeout is the fallback webhook agent-run deadline when config is unset.
+	DefaultAgentTimeout = 600 * time.Second
+	// MaxAgentTimeout caps the configurable webhook agent-run deadline (1h) so a config
+	// typo cannot hold worker/lane slots indefinitely.
+	MaxAgentTimeout = 3600 * time.Second
+)
+
+// ResolveTimeoutSec converts a config value (seconds) into a bounded duration:
+// <= 0 → DefaultAgentTimeout; > 3600 → MaxAgentTimeout; otherwise the value.
+func ResolveTimeoutSec(sec int) time.Duration {
+	if sec <= 0 {
+		return DefaultAgentTimeout
+	}
+	d := time.Duration(sec) * time.Second
+	if d > MaxAgentTimeout {
+		return MaxAgentTimeout
+	}
+	return d
+}