refactor(pi): standalone Zulip gateway service — replaces pi extension

Complete rewrite of the pi Zulip extension as a standalone Node.js service
with direct harness API calls. No longer depends on pi's session — survives
pi shutdown and restart.

Changes:
- src/index.ts: Complete rewrite — standalone process, not a pi extension
  - Direct harness API calls (POST /v1/chat/completions) with conversation memory
  - Per-sender conversation history (up to 50 messages)
  - Placeholder->edit streaming for Zulip DMs
  - Typing indicators via Zulip API
  - Health endpoint on :9200
  - Exponential backoff reconnection
  - Graceful shutdown on SIGINT/SIGTERM
- abiba-zulip.service: systemd service unit file
- README.md: Updated deployment instructions
- package.json/tsconfig.json: Updated for standalone app

Deploy: npm install -> npx tsc -> systemctl enable abiba-zulip
Closes issue #24 (Hermes parity for pi)

pi-zulip-extension/README.md

@@ -0,0 +1,71 @@
+# Abiba Zulip Gateway — Standalone Service
+
+**Replaces** the old pi extension (`~/.pi/agent/extensions/zulip/`).
+
+Instead of injecting messages into pi's session (which dies when pi exits), this
+runs as an independent Node.js **systemd service** that:
+- Polls Zulip event queue for DMs
+- Calls the harness inference API directly (no pi dependency)
+- Maintains per-sender conversation memory
+- Survives pi shutdown and restart
+
+## Architecture
+
+```
+Zulip event queue → poll every 3s → DM detected
+  → send typing indicator + placeholder
+  → POST /v1/chat/completions with conversation history
+  → edit placeholder with final response
+```
+
+## Requirements
+
+- Node.js 22+
+- `npm install` in this directory
+
+## Config
+
+All config via environment variables. Copy `abiba-zulip.service` to set up as a
+systemd service, or run directly:
+
+```bash
+ZULIP_EMAIL=abiba-bot@chat.sysloggh.net \
+ZULIP_API_KEY=your_key \
+ZULIP_SITE=https://chat.sysloggh.net \
+HARNESS_URL=http://192.168.68.116/v1/chat/completions \
+HARNESS_API_KEY=sk-xxx \
+HARNESS_MODEL=qwen3.6-35B-A3B \
+node dist/index.js
+```
+
+## Deploy as a service
+
+```bash
+# 1. Install deps
+cd /opt/abiba-zulip
+npm install
+
+# 2. Build
+npx tsc
+
+# 3. Install systemd service
+cp abiba-zulip.service /etc/systemd/system/
+systemctl daemon-reload
+systemctl enable abiba-zulip
+systemctl start abiba-zulip
+
+# 4. Check status
+systemctl status abiba-zulip
+journalctl -u abiba-zulip -f
+
+# 5. Health check
+curl http://127.0.0.1:9200/health
+```
+
+## Development
+
+```bash
+npm run dev    # watch mode (tsc watch)
+npm run build  # compile
+npm start      # run compiled
+```