fix(cli/session): add command parameter to format_output for JSON envelope spec compliance

The tell function's JSON envelope output was calling format_output(data, fmt)
without a command argument, resulting in an empty 'command' field in the output.
This violates spec compliance because all machine-readable CLI outputs must
include the originating command name in the envelope.

Fix: pass command='agents session tell' to ensure spec-compliant JSON/YAML envelopes.

src/cleveragents/cli/commands/session.py

@@ -859,7 +859,7 @@ def tell(
                     "tool_calls": 0,
                 },
             }
-            typer.echo(format_output(data, fmt))
+            typer.echo(format_output(data, fmt, command="agents session tell"))
             return
 
         if stream: