grammar+db: 3i — not_null_missing diagnostic + TableColumn constraints (ADR-0033 §8.3)

Extend SchemaCache TableColumn with not_null + has_default (with a
TableColumn::new constructor for the common no-constraint case),
populated in build_schema_cache from ColumnDescription (a PK column
counts as not-null). New dml_not_null_missing_diagnostics pass: a
WARNING when a SQL INSERT's explicit column list omits a column that
is NOT NULL with no DEFAULT — advisory (the engine enforces it).
serial/shortid (auto-filled) and defaulted columns are excluded.
Anchored on the target-table ident (no token for the omitted column).

Catalog key diagnostic.not_null_missing (engine-neutral). Tests (+4):
fires on omitted required column; silent when included, when
defaulted, and for auto-gen serial/shortid. ~24 TableColumn literal
sites updated for the two new fields (build clean). 1591 pass / 0
fail / 1 ignored. Clippy clean.

All three ADR-0033 §8 DML diagnostics now implemented. Remaining 3i:
cross-cut verification + #12 UPSERT DO UPDATE validation.

src/runtime.rs

@@ -1002,6 +1002,13 @@ async fn build_schema_cache(database: &Database) -> crate::completion::SchemaCac
                     c.user_type.map(|ty| TableColumn {
                         name: c.name,
                         user_type: ty,
+                        // A PK column is effectively NOT NULL even when
+                        // PRAGMA's notnull flag isn't set on it
+                        // (ADR-0033 §8.3); the not_null_missing pass
+                        // excludes auto-gen types (serial/shortid)
+                        // separately.
+                        not_null: c.notnull || c.primary_key,
+                        has_default: c.default.is_some(),
                     })
                 })
                 .collect();