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/keys.rs

@@ -393,7 +393,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("archive.unsafe_entry", &["entry"]),
     ("archive.zip", &["path", "message"]),
     // ---- DSL failure wrapper / running echo ----
-    ("dsl.failed", &["verb", "subject", "rendered"]),
+    ("dsl.failed", &["rendered"]),
     ("dsl.running", &["input"]),
     // ---- Persistence-fatal banner ----
     ("fatal.persistence", &["operation", "path", "message"]),
@@ -529,7 +529,6 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("ok.rows_deleted", &["count"]),
     ("ok.rows_inserted", &["count"]),
     ("ok.rows_updated", &["count"]),
-    ("ok.summary", &["verb", "subject"]),
     // ---- Client-side success notes (ADR-0017 §6, ADR-0018 §9) ----
     ("client_side.auto_fill_add_serial", &["count"]),
     ("client_side.auto_fill_add_shortid", &["count"]),