create table: column constraints — NOT NULL / UNIQUE / DEFAULT grammar (ADR-0029)

`create table … with pk` now parses the column-constraint
suffix; combined with the commit-1 db layer, a constrained
table works end to end.

- A shared constraint-suffix grammar fragment — `not null`,
  `unique`, `default <literal>` — sits after each column's
  `(type)` group; `build_create_table` walks the matched path
  per column and folds the constraints into `ColumnSpec`.
- §9 redundancy check: every `with pk` column is a primary-key
  column, so `not null` (any) and `unique` (single-column PK)
  are rejected with a friendly error
  (`parse.custom.constraint_redundant_on_pk`).
- `project.yaml` round-trip: `ColumnSchema` gains `not_null` /
  `default`; the YAML reader/writer and `build_read_schema`
  carry them, so `rebuild` / `export` / `import` preserve
  constraints.
- ADR-0029 §2.1's example corrected — `create table` columns
  are all PK columns, so its suffix is for `default` / `check`;
  `docs/simple-mode-limitations.md` records that non-PK
  columns at create time need advanced mode.

CHECK is deferred to the next commit. 1184 tests pass (+7);
clippy clean.

src/friendly/strings/en-US.yaml

@@ -398,6 +398,10 @@ parse:
     # classifies the input as mid-typing rather than
     # dispatching a logically-empty Form C insert.
     insert_form_a_missing_values: "`insert into ...({columns})` looks like Form A — add `values (...)` to supply the matching values."
+    # ADR-0029 §9: a primary-key column is already NOT NULL,
+    # and a single-column primary key is already UNIQUE —
+    # declaring either explicitly is redundant.
+    constraint_redundant_on_pk: "`{column}` is a primary-key column, so it is already {constraint} — drop the redundant constraint."
   # Caret pointer showing where in the input the parser
   # failed. `{padding}` is the leading whitespace; the
   # template appends `^` so the rendered line places the