feat: Hermes Zulip native platform plugin — deprecates old standalone service

Builds on the NousResearch Hermes Agent plugin system:

- plugins/platforms/zulip/ — full BasePlatformAdapter implementation
  - Zulip event queue polling (like pi-zulip-extension)
  - DM-first + @mention + @all-bots routing
  - Placeholder→edit streaming UX
  - Typing indicators
  - Deduplication and echo-loop prevention
  - Auto-registers via register(ctx) — zero core changes
  - plugin.yaml with full env var schema
- hermes-zulip-plugin/DEPRECATED.md — migration guide from old subprocess-based service

Configuration:
  Env vars: ZULIP_SITE, ZULIP_EMAIL, ZULIP_API_KEY (required)
  Config: platforms.zulip.extra in Hermes config.yaml

hermes-zulip-plugin/DEPRECATED.md

@@ -0,0 +1,40 @@
+# DEPRECATED — Hermes Zulip Plugin (Legacy)
+
+**Status:** Deprecated as of 2026-06-25
+**Replaced by:** `plugins/platforms/zulip/` (Hermes native platform plugin)
+
+This directory contains the original standalone Hermes Zulip plugin that ran as a
+systemd service with its own poll loop, subprocess agent invocation, and health
+server.
+
+## Why Deprecated
+
+The new `plugins/platforms/zulip/` plugin is a proper Hermes platform plugin that:
+
+- Extends `BasePlatformAdapter` from the Hermes Gateway
+- Auto-registers via the Hermes plugin system (`register(ctx)`)
+- Uses direct session injection (no subprocess overhead)
+- Leverages Gateway's built-in health checks, config management, and error handling
+- Requires zero changes to core Hermes code
+
+## Migration
+
+Remove the old systemd service and deploy the new plugin:
+
+```bash
+# 1. Stop old service
+systemctl stop zulip-plugin
+systemctl disable zulip-plugin
+
+# 2. Install plugin to ~/.hermes/plugins/platforms/zulip/
+cp -r plugins/platforms/zulip/ ~/.hermes/plugins/platforms/zulip/
+
+# 3. Restart Hermes Gateway
+hermes gateway restart
+```
+
+Config moves from:
+- `/opt/hermes-zulip-plugin/config.yaml` → Hermes `config.yaml` under `platforms: zulip:`
+- Or set `ZULIP_SITE`, `ZULIP_EMAIL`, `ZULIP_API_KEY` env vars
+
+See `plugins/platforms/zulip/plugin.yaml` for configuration reference.