fix(resume): emit structured JSON for /agents --output-format json (#2987)

Resumed /agents --output-format json was returning a human-readable
text render wrapped in a JSON envelope field instead of the actual
structured agent list. The run_resume_command handler was calling
handle_agents_slash_command (text) for the json field instead of
handle_agents_slash_command_json.

Fix: use handle_agents_slash_command_json for the json outcome field,
matching the pattern already used by /skills and /plugins.

Test: extended resumed_inventory_commands_emit_structured_json_when_requested
to cover /agents, asserting kind=="agents", action=="list",
agents is an array, and count is a number (not a text render).

rust/crates/rusty-claude-cli/src/main.rs

@@ -3526,10 +3526,10 @@ fn run_resume_command(
             Ok(ResumeCommandOutcome {
                 session: session.clone(),
                 message: Some(handle_agents_slash_command(args.as_deref(), &cwd)?),
-                json: Some(serde_json::json!({
-                    "kind": "agents",
-                    "text": handle_agents_slash_command(args.as_deref(), &cwd)?,
-                })),
+                json: Some(
+                    serde_json::to_value(handle_agents_slash_command_json(args.as_deref(), &cwd)?)
+                        .unwrap_or_else(|_| serde_json::json!(null)),
+                ),
             })
         }
         SlashCommand::Skills { args } => {