feat(zulip): v3 resilience rewrite — circuit breaker, retry, watchdog, model fix

Root cause: Workers hung because default model was DeepSeek v4-pro (reasoning
model that produces empty content with normal token limits). pi RPC workers
waited forever for content that never arrived.

Changes:
- Circuit breaker (CLOSED→OPEN→HALF_OPEN) around Zulip API calls
- Retry with exponential backoff + jitter for transient errors
- Queue lifecycle management (idle_queue_timeout, auto re-register on BAD_EVENT_QUEUE_ID)
- External supervisor watchdog (restarts router after 3 health check failures)
- Busy worker timeout (SIGKILL after 5 min + error DM)
- PM2 hardening (max_restarts=100, max_memory_restart=500M)
- Crash handlers (uncaughtException + unhandledRejection → reconnect, not die)
- Fixed default model: deepseek-v4-pro → syslog-harness/syslog-auto
- Enhanced health endpoint with circuit breaker stats

Architecture: Research-backed from Zulip event system docs + Node.js resilience
patterns. Inline circuit breaker (no dependency). Separate watchdog process (Hermes pattern).

Verified: Circuit breaker trips on outage, recovers gracefully. End-to-end DM
processed in 4 seconds. Watchdog monitoring every 30s.

pi-zulip-extension/config/settings.json

@@ -0,0 +1,11 @@
+{
+  "lastChangelogVersion": "0.80.6",
+  "defaultProvider": "syslog-harness",
+  "defaultModel": "syslog-auto",
+  "defaultThinkingLevel": "high",
+  "extensions": [
+    "+extensions/mcp/index.ts",
+    "+extensions/zulip/index.js"
+  ],
+  "theme": "dark"
+}