feat: DSL→SQL teaching echo — channel + create-table slice (ADR-0037 + ADR-0038)

Walking skeleton validating the whole echo architecture end to end; the
Command→SQL renderer currently covers `create table`, with the rest of
Bucket A / B / category-3 to follow (ADR-0038 §8).

- Channel (ADR-0037): the three-way EffectiveMode (reusing the existing
  enum, not a new SubmissionMode — recorded in the ADR) rides on
  Action::ExecuteDsl to the runtime. `replay` bypasses the interactive
  spawn, so it never echoes (silent, for free).
- Echo (ADR-0038): built at the runtime's ExecuteDsl dispatch — the worker
  gets decomposed calls, not the Command, so ADR §4's "worker builds it"
  was corrected to the dispatch layer. Gated by echo_for (advanced
  effective mode + DSL-form). Carried on DslSucceeded; rendered by
  note_ok_summary as `Executing SQL: …` immediately beneath `[ok]`. New
  src/echo.rs renderer; echo.executing_sql i18n key.
- command_to_sql: `create table` → `CREATE TABLE T (id serial PRIMARY KEY)`
  (single inline / compound table-level PK), playground type vocabulary,
  round-trip-verified against the advanced walker (the §1 contract).

Tests: echo.rs (render, round-trip contract, mode gate, Sql*-not-echoed);
app.rs (submit carries the 3-way mode; echo renders beneath [ok]).
Suite 1970/0/1; clippy clean.

src/runtime.rs

@@ -384,12 +384,17 @@ async fn run_loop(
                     debug!("quit action received");
                     should_quit = true;
                 }
-                Action::ExecuteDsl { command, source } => {
+                Action::ExecuteDsl {
+                    command,
+                    source,
+                    submission_mode,
+                } => {
                     spawn_dsl_dispatch(
                         session.database().clone(),
                         event_tx.clone(),
                         command,
                         source,
+                        submission_mode,
                     );
                 }
                 Action::JournalFailure { source } => {
@@ -1251,16 +1256,25 @@ fn spawn_dsl_dispatch(
     event_tx: mpsc::Sender<AppEvent>,
     command: Command,
     source: String,
+    submission_mode: crate::app::EffectiveMode,
 ) {
     tokio::spawn(async move {
         // Retain the source for `DslFailed` so the App can journal a
         // rejected command as `err` (ADR-0034 §1/§2).
         let source_for_journal = source.clone();
+        // ADR-0038: the DSL → SQL teaching echo fires for a DSL-form
+        // command submitted in an advanced effective mode (ADR-0037).
+        // `replay` bypasses this spawn (it calls `execute_command_typed`
+        // directly), so replayed lines never echo. Built before execution
+        // from the Command; resolved-name / category-3 forms (Bucket B/§6,
+        // later slices) will additionally read the execution result.
+        let echo = crate::echo::echo_for(&command, submission_mode);
         let outcome = execute_command_typed(&database, command.clone(), source).await;
         let event = match outcome {
             Ok(CommandOutcome::Schema(description)) => AppEvent::DslSucceeded {
                 command: command.clone(),
                 description,
+                echo,
             },
             Ok(CommandOutcome::SchemaSkipped(description)) => AppEvent::DslCreateSkipped {
                 command: command.clone(),