Add platform-specific formatting hints and identity for AIAgent

- Introduced a default agent identity prompt to ensure consistent behavior across platforms.
- Added platform-specific formatting hints for CLI, WhatsApp, Telegram, and Discord to guide the agent's output style.
- Updated the AIAgent initialization to accept a platform parameter, enhancing adaptability to different interfaces.

cli.py

@@ -662,6 +662,7 @@ class HermesCLI:
                 quiet_mode=True,  # Suppress verbose output for clean CLI
                 ephemeral_system_prompt=self.system_prompt if self.system_prompt else None,
                 session_id=self.session_id,  # Pass CLI's session ID to agent
+                platform="cli",  # CLI interface — agent uses terminal-friendly formatting
             )
             return True
         except Exception as e: