feat(hermes): complete Zulip gateway platform adapter plugin

Rewrite hermes-zulip-plugin as a proper Hermes platform plugin with
auto-discovery via plugin.yaml + __init__.py + register() pattern.

Features:
- Zulip event queue registration and polling for real-time messages
- DM-first architecture — private messages route into agent's session
- Placeholder→edit streaming UX (Thinking... → final response)
- Typing indicators via Zulip API
- Exponential backoff reconnection and queue re-registration
- Message deduplication with sliding window
- Config via config.yaml or env vars (ZULIP_EMAIL, ZULIP_API_KEY, ZULIP_SITE)
- Standalone sender for cron/notification delivery
- Plugin auto-discovery via @hermes_agent.plugins entry point

Architecture follows the proven ntfy adapter pattern:
  plugins/platforms/{name}/plugin.yaml
  plugins/platforms/{name}/__init__.py  → exports register()
  plugins/platforms/{name}/adapter.py   → ZulipAdapter(BasePlatformAdapter)

Deployment: copy to ~/.hermes/plugins/platforms/zulip/ and restart gateway
Requirements: pip install zulip httpx

Closes issue #24

hermes-zulip-plugin/plugin.yaml

@@ -0,0 +1,47 @@
+name: zulip-platform
+label: Zulip
+kind: platform
+version: 1.0.0
+description: >
+  Zulip messaging gateway adapter for Hermes Agent.
+  Connects to any Zulip server, registers an event queue, and polls for
+  incoming messages. Handles DMs first (ADR-001), with @mention support
+  planned. Uses the Zulip Python SDK for API access.
+
+  DM-first architecture: private messages route directly into the Hermes
+  agent's session, so the same personality and conversation continuity
+  is maintained between TUI, CLI, and Zulip.
+
+  Features: event queue polling, typing indicators, placeholder→edit
+  streaming, exponential backoff reconnection, health endpoint.
+author: Syslog Solution LLC
+requires_env:
+  - name: ZULIP_EMAIL
+    description: "Zulip bot email address (e.g. tanko-bot@chat.sysloggh.net)"
+    prompt: "Zulip bot email"
+    password: false
+  - name: ZULIP_API_KEY
+    description: "Zulip bot API key"
+    prompt: "Zulip API key"
+    password: true
+  - name: ZULIP_SITE
+    description: "Zulip server URL (e.g. https://chat.sysloggh.net)"
+    prompt: "Zulip server URL"
+    password: false
+optional_env:
+  - name: ZULIP_ALLOWED_USERS
+    description: "Comma-separated Zulip user IDs or emails allowed to DM the agent"
+    prompt: "Allowed users (comma-separated emails or IDs)"
+    password: false
+  - name: ZULIP_ALLOW_ALL_USERS
+    description: "Allow any user to DM the bot (disables allowlist)"
+    prompt: "Allow all users? (true/false)"
+    password: false
+  - name: ZULIP_HOME_CHANNEL
+    description: "Default recipient for cron / notification delivery"
+    prompt: "Home channel user email (or empty)"
+    password: false
+  - name: ZULIP_HOME_CHANNEL_NAME
+    description: "Human label for the home channel"
+    prompt: "Home channel display name"
+    password: false