feat: ADR-0035 4b — foreign keys in CREATE TABLE

Add foreign keys to advanced-mode SQL CREATE TABLE — the SQL spelling of
an ADR-0013 named relationship, created in the same transaction as the
table (one undo step).

- Grammar: inline `<col> … REFERENCES <parent>[(<col>)] [ON DELETE/UPDATE
  …]` (a new column constraint) and table-level `[CONSTRAINT <name>]
  FOREIGN KEY (<col>) REFERENCES …` (two new element branches — both
  start on a concrete keyword, never a leading Optional, which would
  abort the element Choice). Referential clauses reuse
  shared::REFERENTIAL_CLAUSES.
- Builder: greedy FK-clause consumption (parens consumed internally so
  they don't perturb the 4a.3 element-boundary depth tracker); inline FK
  auto-named, table FK takes an optional CONSTRAINT name.
- Worker: do_create_table resolves + validates each FK before building
  the DDL (self-ref validates against the in-statement columns/PK; bare
  REFERENCES resolves to the parent's single-column PK, composite ->
  error; PK-target + Type::fk_target_type compatibility), emits the
  FOREIGN KEY clause identically to schema_to_ddl, and writes the
  relationship metadata in the create transaction.
- Reuse: name/uniqueness/metadata-insert/type-compat factored into shared
  helpers; do_add_relationship refactored to use them.
- FKs round-trip via the existing relationship plumbing (no new
  persistence structures); describe surfaces the relationship.

Self-references and bare `REFERENCES <parent>` supported (user-confirmed).
Self-ref pre-submit indicator wrinkle deferred to 4i (tracked in ADR §13,
a code comment, and the plan).

DA/runda round added cross-cutting probes (FK survives the add-column
rebuild + a later rebuild_from_text; referential actions survive rebuild;
drop-child clears the relationship; drop-parent refused; bare self-ref
resolves to own PK) — all green, no fixes needed.

27 new tests (grammar/builder + Tier-3). Docs: ADR-0035 Status/§13,
README, requirements.md Q1.

Tests: 1795 passing, 0 failing, 1 ignored. Clippy clean.

docs/adr/0035-advanced-mode-sql-ddl.md

@@ -3,12 +3,13 @@
 ## Status
 
 Accepted. Design agreed with the user (2026-05-24); the approach is
-**validated end-to-end by sub-phases 4a / 4a.2 / 4a.3** (`CREATE TABLE`
-with column- and table-level constraints, implemented 2026-05-25 —
-plans `docs/plans/20260524-adr-0035-sql-ddl-4a.md`,
-`…-4a2.md`, `…-4a3.md`), so the decision is accepted while the remaining
-sub-phases (**4b–4i**, §13) continue. This is **Phase 4** of the
-ADR-0030 roadmap (the
+**validated end-to-end by sub-phases 4a / 4a.2 / 4a.3 / 4b**
+(`CREATE TABLE` with column- and table-level constraints and foreign
+keys, implemented 2026-05-25 — plans
+`docs/plans/20260524-adr-0035-sql-ddl-4a.md`, `…-4a2.md`, `…-4a3.md`,
+`docs/plans/20260525-adr-0035-sql-ddl-4b.md`), so the decision is
+accepted while the remaining sub-phases (**4c–4i**, §13) continue. This
+is **Phase 4** of the ADR-0030 roadmap (the
 advanced-mode SQL surface), the peer of ADR-0031 (expression grammar),
 ADR-0032 (`SELECT`), and ADR-0033 (DML). It **clarifies ADR-0030 §4**
 on how DDL is represented and executed.
@@ -351,8 +352,21 @@ ADR-0033's structure:
   introduces a structure simple mode could never produce, or an
   expression the structural helper cannot consume — cf. the
   `UNIQUE`-index flag in 4d and the rename op in 4h.)
-- **4b — Foreign keys in `CREATE TABLE`.** Inline `REFERENCES` +
-  table-level `FOREIGN KEY` → relationship metadata, one undo step.
+- **4b — Foreign keys in `CREATE TABLE`.** *(Implemented 2026-05-25 —
+  plan `docs/plans/20260525-adr-0035-sql-ddl-4b.md`.)* Inline
+  `REFERENCES <parent>[(<col>)] [ON DELETE/UPDATE …]` + table-level
+  `[CONSTRAINT <name>] FOREIGN KEY (<col>) REFERENCES …` → ADR-0013
+  relationship metadata, written in the create transaction (one undo
+  step). Reuses the relationship name/uniqueness/metadata helpers
+  shared with `add relationship`; `do_create_table` emits the
+  `FOREIGN KEY` clause identically to `schema_to_ddl`. **Self-references**
+  (parent = the table being created, validated against the in-statement
+  columns/PK) and the **bare `REFERENCES <parent>`** form (resolves to
+  the parent's single-column PK; composite → error) are both supported
+  (user-confirmed). Inline FKs are auto-named; only the table-level form
+  takes `CONSTRAINT <name>`. PK-target only (UNIQUE-target deferred with
+  `add relationship`); `Type::fk_target_type` (ADR-0011) governs type
+  compatibility.
 - **4c — `DROP TABLE [IF EXISTS]`** → `SqlDropTable` (cascade parity;
   `IF EXISTS` no-op-with-note, §4).
 - **4d — `CREATE [UNIQUE] INDEX` / `DROP INDEX`** → `SqlCreateIndex`
@@ -370,7 +384,17 @@ ADR-0033's structure:
 - **4h — `ALTER TABLE … RENAME TO`** (the §6 new low-level op).
 - **4i — Verification sweep.** Typing-surface + matrix coverage,
   engine-neutral error pass, undo-parity check (one step per
-  statement), `help`/usage for the new forms.
+  statement), `help`/usage for the new forms. **Carried in from earlier
+  slices:** (a) refresh the `CREATE TABLE` help/usage skeleton for the
+  4a.2 `DEFAULT`/`CHECK`/composite-`UNIQUE`, 4a.3 table-`CHECK`, and 4b
+  FK forms (deferred from each); (b) `describe` display of table-level
+  constraints (composite `UNIQUE` + table `CHECK`); (c) **4b self-ref
+  FK indicator** — a `CREATE TABLE` with a self-referencing FK
+  (`references <self>`) parses + executes correctly, but the pre-submit
+  schema-existence diagnostic falsely flags the not-yet-created self
+  table as unknown (the FK parent slot is `IdentSource::Tables`). Make
+  the diagnostic treat a FK parent equal to the `CREATE TABLE` target as
+  valid, so the indicator stops lying for self-references.
 
 ## Consequences