feat: replace the [ok] summary line with a ✓/✗ echo marker

An audit of the command surface found the `[ok] <verb> <subject>`
summary line duplicated the echo line above it everywhere; its only
unique signal was success-vs-error. Retire it: a command's echo line
now resolves from `running: <input>` to `<input> ✓` / `<input> ✗`
on completion, and the symmetric `"<verb> <subject>" failed:` prefix
is dropped (only the reason remains). Content lines (row counts,
structure, plan tree, teaching echo) are unchanged.

Echo lines carry an EchoStatus; executed commands push Pending and
resolve the oldest-pending echo on their result event (FIFO worker —
correct under interleaving). Parse-time and pre-flight rejections are
not executed and keep their running: + caret rendering. App-command
[ok] lines (rebuild/export/replay) are payload-bearing and untouched.
ADR-0040.

src/friendly/strings/en-US.yaml

@@ -665,12 +665,15 @@ project:
 
 # ---- DSL failure wrapper + advanced-mode placeholder + fatal --------
 dsl:
-  # Wrapper around the friendly-error layer's translated
-  # message, surfaced as `"<verb> <subject>" failed: <rendered>`.
-  failed: '"{verb} {subject}" failed: {rendered}'
+  # The friendly-error layer's translated reason, shown beneath the
+  # failed command's echo line. ADR-0040: the redundant
+  # `"<verb> <subject>" failed:` prefix was dropped — the echo line
+  # carries the ✗ marker and names the command.
+  failed: "{rendered}"
   # Echo line `running: <input>` shown above each command's
-  # response so the user has on-screen context for the
-  # output that follows.
+  # response while it executes; ADR-0040 resolves it to
+  # `<input> ✓` / `<input> ✗` on completion (the marker replaces
+  # the old `[ok] <verb> <subject>` summary line).
   running: "running: {input}"
 
 # ---- Value-validation errors (per-column at bind time) --------------
@@ -916,12 +919,11 @@ db:
 # locale lands.)
 
 ok:
-  # Generic `[ok] <verb> <subject>` header used for every
-  # successful DSL command. Verbs come from `Command::verb()`
-  # (already English keywords); subjects are the table /
-  # relationship endpoints derived in `Command::display_subject()`.
-  summary: "[ok] {verb} {subject}"
-  # Per-operation row-count footers shown beneath the summary.
+  # ADR-0040: the generic `[ok] <verb> <subject>` summary line was
+  # retired — a successful command's echo line now carries a ✓
+  # marker (the verb+subject duplicated the echo above it). The
+  # per-operation row-count footers below still convey real payload
+  # and are unchanged.
   rows_inserted: "  {count} row(s) inserted"
   rows_updated: "  {count} row(s) updated"
   rows_deleted: "  {count} row(s) deleted"