Accept the CLI snapshots the engine flag and the listed diagnostics changed

The create error now names each validation diagnostic as `rule: message`
after "Validation failed", and `fabro server start --help` lists
`--engine`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

lib/apps/fabro-cli/tests/it/cmd/create.rs

@@ -1497,7 +1497,7 @@ fn create_invalid_workflow_fails_without_creating_run() {
     ----- stdout -----
     ----- stderr -----
       × could not create run
-      ╰─▶ run intent could not be compiled: Validation failed
+      ╰─▶ run intent could not be compiled: Validation failed: start_node: Pipeline must have exactly one start node (shape=Mdiamond or id start/Start); exit_no_outgoing: Exit node 'exit' has 1 outgoing edge(s) but must have none
     ");
 
     let run_count = run_count_for_test_case(&context);
@@ -1523,7 +1523,7 @@ fn create_rejects_unbound_template_inputs_without_creating_run() {
     ----- stdout -----
     ----- stderr -----
       × could not create run
-      ╰─▶ run intent could not be compiled: Validation failed
+      ╰─▶ run intent could not be compiled: Validation failed: template_undefined_variable: undefined template variable `inputs.app_dir` in graph attribute `goal`; template_undefined_variable: undefined template variable `inputs.app_dir` in node `work` attribute `prompt`
     ");
 
     let run_count = run_count_for_test_case(&context);

lib/apps/fabro-cli/tests/it/cmd/server_start.rs

@@ -212,6 +212,8 @@ fn help() {
               Named environment for agent tools
           --max-concurrent-runs <MAX_CONCURRENT_RUNS>
               Maximum number of concurrent run executions
+          --engine <ENGINE>
+              The engine for every run whose workflow version names none (`legacy` or `petri`); overrides `[server.execution] engine`
           --config <CONFIG>
               Path to server config file (default: ~/.fabro/settings.toml)
       -h, --help