fix: use .get() for env_vars key in _show_tool_availability_warnings

Fixes KeyError: 'missing_vars' crash on CLI startup when toolsets are
unavailable. registry.py returns dicts with 'env_vars' key, but
_show_tool_availability_warnings() was accessing 'missing_vars' directly.

Now uses .get("env_vars") or .get("missing_vars") to handle both key
names, consistent with how doctor.py already handles this.

Fixes #834

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cli.py

@@ -3611,8 +3611,8 @@ class HermesCLI:
             available, unavailable = check_tool_availability()
             
             # Filter to only those missing API keys (not system deps)
-            api_key_missing = [u for u in unavailable if u["missing_vars"]]
-            
+            api_key_missing = [u for u in unavailable if u.get("env_vars") or u.get("missing_vars")]
+
             if api_key_missing:
                 self.console.print()
                 self.console.print("[yellow]⚠️  Some tools disabled (missing API keys):[/]")
@@ -3620,7 +3620,8 @@ class HermesCLI:
                     tools_str = ", ".join(item["tools"][:2])  # Show first 2 tools
                     if len(item["tools"]) > 2:
                         tools_str += f", +{len(item['tools'])-2} more"
-                    self.console.print(f"   [dim]• {item['name']}[/] [dim italic]({', '.join(item['missing_vars'])})[/]")
+                    env_vars = item.get("env_vars") or item.get("missing_vars") or []
+                    self.console.print(f"   [dim]• {item['name']}[/] [dim italic]({', '.join(env_vars)})[/]")
                 self.console.print("[dim]   Run 'hermes setup' to configure[/]")
         except Exception:
             pass  # Don't crash on import errors