feat: enhance README and improve environment configuration

- Added a new section in the README for Inference Providers, detailing setup instructions for Nous Portal, OpenRouter, and Custom Endpoints, improving user guidance for LLM connections.
- Updated messaging platform setup instructions to include Slack and WhatsApp, providing clearer steps for configuration.
- Introduced a new environment variable, TERMINAL_SANDBOX_DIR, to allow users to customize the sandbox storage location for Docker and Singularity environments.
- Refactored the Docker and Singularity environment classes to utilize the new sandbox directory for persistent workspaces, enhancing organization and usability.
- Improved handling of working directories across various environments, ensuring compatibility and clarity in execution paths.

tools/environments/base.py

@@ -1,7 +1,24 @@
 """Base class for all Hermes execution environment backends."""
 
 from abc import ABC, abstractmethod
+import os
 import subprocess
+from pathlib import Path
+
+
+def get_sandbox_dir() -> Path:
+    """Return the host-side root for all sandbox storage (Docker workspaces,
+    Singularity overlays/SIF cache, etc.).
+
+    Configurable via TERMINAL_SANDBOX_DIR. Defaults to ~/.hermes/sandboxes/.
+    """
+    custom = os.getenv("TERMINAL_SANDBOX_DIR")
+    if custom:
+        p = Path(custom)
+    else:
+        p = Path.home() / ".hermes" / "sandboxes"
+    p.mkdir(parents=True, exist_ok=True)
+    return p
 
 
 class BaseEnvironment(ABC):