docs: add /insights to all help menus and documentation

- website/docs/reference/cli-commands.md: Added 'hermes insights' terminal
  command section with --days and --source flags, plus /insights slash command
  in the Conversation section
- website/docs/user-guide/cli.md: Added /insights to slash commands table
- website/docs/user-guide/messaging/index.md: Added /insights to gateway
  chat commands table
- website/docs/user-guide/sessions.md: Added cross-reference to hermes
  insights from the sessions stats section

website/docs/reference/cli-commands.md

@@ -108,6 +108,14 @@ These are commands you run from your shell.
 | `hermes sessions prune` | Remove old sessions |
 | `hermes sessions stats` | Show session statistics |
 
+### Insights
+
+| Command | Description |
+|---------|-------------|
+| `hermes insights` | Show usage analytics for the last 30 days |
+| `hermes insights --days 7` | Analyze a custom time window |
+| `hermes insights --source telegram` | Filter by platform |
+
 ---
 
 ## Slash Commands (Inside Chat)
@@ -145,6 +153,7 @@ Type `/` in the interactive CLI to see an autocomplete dropdown.
 | `/save` | Save the current conversation |
 | `/compress` | Manually compress conversation context |
 | `/usage` | Show token usage for this session |
+| `/insights [--days N]` | Show usage insights and analytics (last 30 days) |
 
 ### Media & Input