feat(render): incidental-DDL confirmations show structure only, no relationships (#28)

Per ADR-0050 (closing issue #28): the confirmation echo after an
incidental structural edit — create table, add/drop/rename/change
column, add/drop index — now renders the structure only (header +
column box + indexes + constraints) and no longer appends the
References:/Referenced by: relationship block.

Rationale: a confirmation reports the change just made, not the
table's relationships, which the user didn't touch. Relationship info
is still one `show table <T>` away, and the relationship-subject
surfaces (show table, add/drop relationship) keep their ADR-0044
diagrams unchanged.

Scope is all incidental DDL (user-confirmed). Mechanism: drop the
relationship-block call from render_structure (all its callers are
incidental DDL); the handle_dsl_success diagram-vs-structure routing
is unchanged. The orphaned relationship_prose_lines + cols_disp
helpers are deleted (the prose format survives in ADR-0016 §5 + git
history for a future OOS-7 always-prose setting).

ADR-0050 supersedes ADR-0044 §1's incidental-DDL prose clause and the
relationship-block half of ADR-0016 §5 (both annotated). Tests: prose-
presence unit test + snapshot removed; new unit test locks structure-
only with inbound+outbound relationships present; the misnamed add-
column integration test inverted + renamed. 2458 pass / 0 fail / 0
skip, clippy clean.

docs/adr/0044-relationship-visualization.md

@@ -103,6 +103,10 @@ Prose-retained surfaces (**unchanged** from ADR-0016 §5):
   `add`/`drop index` — keep the terse `References:` /
   `Referenced by:` prose. A simple `add column` on a heavily-related
   table should not print a wall of diagrams.
+  *(**Superseded 2026-06-12 by ADR-0050** (issue #28): these incidental
+  DDL echoes now render **structure only** — no relationship block at
+  all, neither prose nor diagram. The prose renderer was deleted. The
+  diagram surfaces below are unchanged.)*
 
 So this **partially supersedes ADR-0016 §5**: the prose block is
 replaced by diagrams on the relationship-subject surfaces and