fix(#834): KeyError 'missing_vars' crashes CLI startup

Fix _show_tool_availability_warnings() to use 'env_vars' key
instead of 'missing_vars' which doesn't exist in registry output.

Closes #834

cli.py

@@ -3611,7 +3611,7 @@ 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")]
             
             if api_key_missing:
                 self.console.print()
@@ -3620,7 +3620,7 @@ 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'])})[/]")
+                    self.console.print(f"   [dim]• {item['name']}[/] [dim italic]({', '.join(item['env_vars'])})[/]")
                 self.console.print("[dim]   Run 'hermes setup' to configure[/]")
         except Exception:
             pass  # Don't crash on import errors