feat: DSL→SQL teaching echo — Bucket A renderer (ADR-0038 Phase 1)

Expands the renderer skeleton from ADR-0038's first slice to the full
single-statement catalogue. Every Bucket A row round-trips through the
advanced-mode walker (the §1 copy-paste contract):

  add column / drop column (non-cascade) / rename column / change column
  (SET DATA TYPE) / add constraint (not null, default, unique, check) /
  drop constraint (not null, default) / show data [where] [limit] /
  delete --all-rows / update --all-rows

Adds the Expr→SQL and Value→SQL-literal renderers (ADR-0038 §5) — bare
identifiers, inlined literals, NULL uppercase, standard <> for inequality
— and threads `echo: Option<String>` onto the six remaining success
events (DslAddColumn/DropColumn/ChangeColumn/Data/Update/Delete
Succeeded) with matching runtime construction and App stash arms.

`show data` is the one Bucket A row whose echo needs schema info beyond
the Command (the `ORDER BY <pk>` for a limited query): the pure
renderer takes the primary key as a parameter, and the runtime sources
it post-execution via describe_table — gated on advanced mode + limit
present, mirroring the enrich_dsl_failure describe pattern. An
end-to-end test pins the describe→PK→ORDER BY glue against a real
worker; the simple-mode gate and unlimited-no-lookup paths are covered
too.

Also fixes a contract gap surfaced while completing the catalogue: the
existing create-table echo silently dropped per-column DEFAULT / CHECK,
which simple-mode `create table … with pk c(ty) check (…)` does parse
(ADR-0029) — so the echo was non-equivalent. The render now emits the
full ADR-0029 column-constraint suffix, sharing one append_constraints
helper with `add column`.

Phase 2 (Bucket B — resolved-name + multi-line echoes, including
`add index`), Phase 3 (category-3 prose), and the de-emphasised
styled-runs polish remain deferred per ADR-0038 §8 phasing.

Tests: 2000 passed / 0 failed / 1 ignored (pre-existing); clippy clean
(`--all-targets -D warnings`, nursery).

src/event.rs

@@ -61,8 +61,15 @@ pub enum AppEvent {
         command: Command,
         name: String,
     },
-    /// A `show data` query succeeded.
-    DslDataSucceeded { command: Command, data: DataResult },
+    /// A `show data` query succeeded. `echo` is the DSL → SQL teaching
+    /// echo (ADR-0038) — built post-execution because the limited form
+    /// orders by the table's primary key (handoff §5). `None` for a
+    /// SQL-entered `SELECT` or any simple-mode submission.
+    DslDataSucceeded {
+        command: Command,
+        data: DataResult,
+        echo: Option<String>,
+    },
     /// An `explain …` command succeeded (ADR-0028). `plan`
     /// carries the captured query plan; nothing was executed.
     DslExplainSucceeded { command: Command, plan: QueryPlan },
@@ -73,10 +80,18 @@ pub enum AppEvent {
     DslUpdateSucceeded {
         command: Command,
         result: UpdateResult,
+        /// The DSL → SQL teaching echo (ADR-0038): `UPDATE T SET …` for an
+        /// `update … --all-rows` fall-through. `None` for a SQL-entered
+        /// `UPDATE` or any simple-mode submission.
+        echo: Option<String>,
     },
     DslDeleteSucceeded {
         command: Command,
         result: DeleteResult,
+        /// The DSL → SQL teaching echo (ADR-0038): `DELETE FROM T` for a
+        /// `delete … --all-rows` fall-through. `None` for a SQL-entered
+        /// `DELETE` or any simple-mode submission.
+        echo: Option<String>,
     },
     /// A `change column …` succeeded. `result` carries both the
     /// post-rebuild description (for the auto-show) and the
@@ -84,6 +99,10 @@ pub enum AppEvent {
     DslChangeColumnSucceeded {
         command: Command,
         result: ChangeColumnTypeResult,
+        /// The DSL → SQL teaching echo (ADR-0038): `ALTER TABLE T ALTER
+        /// COLUMN c SET DATA TYPE …`. `None` in simple mode. (The
+        /// `--dont-convert` caveat line is category-3, a later slice.)
+        echo: Option<String>,
     },
     /// An `add column …` succeeded. `result` carries the
     /// post-add description plus any `[client-side]` notes
@@ -91,6 +110,9 @@ pub enum AppEvent {
     DslAddColumnSucceeded {
         command: Command,
         result: AddColumnResult,
+        /// The DSL → SQL teaching echo (ADR-0038): `ALTER TABLE T ADD
+        /// COLUMN c <ty> …`. `None` in simple mode.
+        echo: Option<String>,
     },
     /// A `drop column …` succeeded. `result` carries the
     /// post-drop description plus the names of any indexes
@@ -98,6 +120,10 @@ pub enum AppEvent {
     DslDropColumnSucceeded {
         command: Command,
         result: DropColumnResult,
+        /// The DSL → SQL teaching echo (ADR-0038): `ALTER TABLE T DROP
+        /// COLUMN c` for a plain (non-`--cascade`) drop. `None` in simple
+        /// mode, and for `--cascade` (a multi-statement echo, Phase 2).
+        echo: Option<String>,
     },
     /// A DSL command failed. `error` is the structured
     /// payload, `facts` is the runtime-built schema-resolved