docs: comprehensive documentation update for recent features

New documentation:
- DingTalk messaging platform setup guide (dingtalk.md)

Updated existing docs:
- quickstart.md: add Alibaba Cloud, Kilo Code, Vercel AI Gateway to provider table
- configuration.md: add Alibaba Cloud provider, website blocklist config,
  light/dark theme mode, smart approvals (ask/smart/off)
- environment-variables.md: add Mattermost, Matrix, DingTalk, Browser Use,
  DashScope env vars
- browser.md: add Browser Use cloud provider, /browser connect CDP mode,
  multi-provider architecture, fix limitation section contradiction
- slash-commands.md: add /tools enable/disable/list, /browser connect/disconnect/status
- messaging/index.md: add DingTalk, Mattermost, Matrix to architecture diagram,
  platform toolset table, security allowlists, and Next Steps links
- security.md: add website access policy (blocklist) documentation
- sidebars.ts: add Mattermost, Matrix, DingTalk to Messaging Gateway sidebar

website/docs/user-guide/security.md

@@ -277,6 +277,25 @@ Error messages from MCP tools are sanitized before being returned to the LLM. Th
 - Bearer tokens
 - `token=`, `key=`, `API_KEY=`, `password=`, `secret=` parameters
 
+### Website Access Policy
+
+You can restrict which websites the agent can access through its web and browser tools. This is useful for preventing the agent from accessing internal services, admin panels, or other sensitive URLs.
+
+```yaml
+# In ~/.hermes/config.yaml
+website_blocklist:
+  enabled: true
+  domains:
+    - "*.internal.company.com"
+    - "admin.example.com"
+  shared_files:
+    - "/etc/hermes/blocked-sites.txt"
+```
+
+When a blocked URL is requested, the tool returns an error explaining the domain is blocked by policy. The blocklist is enforced across `web_search`, `web_extract`, `browser_navigate`, and all URL-capable tools.
+
+See [Website Blocklist](/docs/user-guide/configuration#website-blocklist) in the configuration guide for full details.
+
 ### Context File Injection Protection
 
 Context files (AGENTS.md, .cursorrules, SOUL.md) are scanned for prompt injection before being included in the system prompt. The scanner checks for: