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/abiba-zulip.service

@@ -0,0 +1,48 @@
+[Unit]
+Description=Abiba Zulip Gateway Service — Standalone Zulip bot for pi agent
+Documentation=https://git.sysloggh.net/SyslogSolution/zulip-platform-plugins
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=root
+WorkingDirectory=/opt/abiba-zulip
+
+# ── Zulip credentials ─────────────────────────────────────────────────────
+Environment=ZULIP_EMAIL=abiba-bot@chat.sysloggh.net
+Environment=ZULIP_API_KEY=cKTDMZAPW08dk3zl05sStzO7HRztzyn8
+Environment=ZULIP_SITE=https://chat.sysloggh.net
+
+# ── Agent identity ─────────────────────────────────────────────────────────
+Environment=AGENT_NAME=abiba
+Environment=AGENT_OWNER_EMAIL=jerome@sysloggh.com
+
+# ── Harness API (inference) ────────────────────────────────────────────────
+Environment=HARNESS_URL=http://192.168.68.116/v1/chat/completions
+Environment=HARNESS_API_KEY=sk-856ffb0bbb-e5aaf78b10054eca608f8fbcbd73a889
+Environment=HARNESS_MODEL=qwen3.6-35B-A3B
+Environment=HARNESS_MAX_TOKENS=4096
+
+# ── Service config ─────────────────────────────────────────────────────────
+Environment=HEALTH_PORT=9200
+Environment=POLL_INTERVAL_MS=3000
+Environment=MAX_RETRIES=5
+Environment=RETRY_DELAY_MS=5000
+
+ExecStart=/usr/bin/node /opt/abiba-zulip/dist/index.js
+Restart=always
+RestartSec=5
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+
+# Security hardening (optional — adjust as needed)
+NoNewPrivileges=true
+ProtectHome=read-only
+ProtectSystem=full
+PrivateTmp=true
+
+[Install]
+WantedBy=multi-user.target