Phase D: insert value list mirrors do_insert's user_cols contract

Bug: hint at \`insert into Customers values (\` for a Customers
table with id:serial PK suggested typing an integer for \`id\`,
but the dispatch path (\`db::do_insert\`) deliberately doesn't
accept user-supplied values for auto-generated columns in
Form B. The grammar prompted for a value the dispatch would
refuse.

The fix aligns Phase D's \`column_value_list\` dynamic sub-grammar
with do_insert's three forms (ADR-0014 + ADR-0018 §3):

- **Form A** \`insert into <T> (col1, col2, …) values (…)\` —
  user explicitly lists columns. Slot list mirrors that
  selection; serial / shortid columns CAN appear if the user
  lists them.
- **Form B** \`insert into <T> values (…)\` — bare values. Slot
  list = non-auto-generated columns of the table in
  declaration order. Serial / shortid get auto-filled by the
  dispatch; the grammar doesn't prompt for them.
- **Form C** \`insert into <T> (v1, v2, …)\` — bare value list.
  Not affected by this change (column_value_list isn't on this
  path; Form C's literals route through the schemaless
  INSERT_PAREN_LIST).

Implementation:

\`WalkContext.user_listed_columns: Option<Vec<String>>\` — when
\`Some\`, signals Form A; \`None\` is Form B. Populated by walking
the first paren's column-list idents.

\`Node::Ident.writes_user_listed_column: bool\` — new field;
\`true\` on the INSERT_PAREN_ITEM's Ident child. When the
walker matches that ident in Form A, it appends the
schema-canonical column name (case-corrected against the
schema) to user_listed_columns.

\`column_value_list\` factory:
- If user_listed_columns is Some → resolve each name from the
  schema; one typed slot per listed column.
- Else → filter current_table_columns to non-auto-generated;
  one typed slot per remaining column.
- Empty result → fall back to the schemaless value-literal
  list (a serial-only table in Form B has nothing for the
  user to type).

Tests:
- New \`phase_d_insert_form_b_skips_serial_column\` confirms the
  bug: \`insert into Customers values (1, 'Alice')\` against a
  Customers with serial id rejects at parse time (Form B
  expects 1 value for Name, not 2).
- New \`phase_d_insert_form_a_accepts_serial_when_listed\`
  confirms \`insert into Customers (id, Name) values (1, 'Alice')\`
  works.
- New \`phase_d_insert_form_a_filters_to_user_listed_columns\`
  confirms partial Form A (\`(Name) values ('Alice')\`).
- Updated \`phase_d_insert_with_schema_accepts_typed_values_per_column\`
  to match the new Form B contract (2 user-typed values, not 3).
- Updated typed-hint test matrix split into form-B (8 types)
  and form-A (serial / shortid).
- New \`typed_hint_form_b_skips_serial_column_to_generic_or_text_neighbor\`
  pins the fallback behavior for a serial-only table.

For the user: \`insert into Customers values (\` for a Customers
with \`(id:serial, Name:text, Email:text)\` now hints
\`for \`Name\`: Type a quoted string …\` (skipping id entirely)
and accepts exactly 2 values. To set the serial explicitly,
use Form A: \`insert into Customers (id, Name, Email) values
(1, 'Alice', 'a@b.c')\`.

Tests: 851 passing, 0 failing, 1 ignored. Clippy clean.

src/friendly/strings/en-US.yaml

@@ -301,8 +301,13 @@ hint:
   value_slot_date: "Type a quoted date as 'YYYY-MM-DD' or null"
   value_slot_datetime: "Type a quoted datetime as 'YYYY-MM-DD HH:MM:SS' or null"
   value_slot_blob: "Type a quoted blob literal or null"
-  value_slot_serial: "Type an integer (or omit to auto-generate) or null"
-  value_slot_shortid: "Type a quoted shortid (or omit to auto-generate) or null"
+  # Serial / shortid in `values (…)` form: the user must enter
+  # something at this position (no "skip column" syntax). `null`
+  # is the auto-fill path (ADR-0018: serial / shortid columns
+  # auto-fill null cells on insert), so the prose leads with
+  # null and offers an explicit value as the alternative.
+  value_slot_serial: "Type null to auto-generate, or an explicit integer"
+  value_slot_shortid: "Type null to auto-generate, or a quoted shortid"
   # Wrapper that prefixes a per-column-type slot hint with the
   # actual column name so the user sees "for `Email`: Type a
   # quoted string …" instead of the generic type prose.