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/persistence/mod.rs

@@ -145,6 +145,13 @@ pub struct ColumnSchema {
     /// save/load cycle. Defaults to `false` when missing in
     /// older project files.
     pub unique: bool,
+    /// `NOT NULL` constraint (ADR-0029). Defaults to `false`
+    /// when missing in older project files.
+    pub not_null: bool,
+    /// `DEFAULT` expression as a SQL literal (ADR-0029) — the
+    /// form SQLite reports and `schema_to_ddl` echoes verbatim.
+    /// `None` when the column has no default.
+    pub default: Option<String>,
 }
 
 /// One index as recorded in `project.yaml` (ADR-0025).
@@ -374,6 +381,8 @@ mod tests {
                 name: "Name".to_string(),
                 user_type: Type::Text,
                 unique: false,
+                not_null: false,
+                default: None,
             }],
             rows: vec![vec![CellValue::Text("Alice".to_string())]],
         };