feat(seed): set override clause + column-fill (ADR-0048 Phase 2)

Build the two SD2 surfaces Phase 1 deferred:

- `set` override clause (D2): comma-separated per-column pins —
  `= 'v'` (fixed), `in ('a','b')` (pick-list), `as <generator>`
  (named), `between x and y` (range; numeric and quoted dates).
  Type-aware via the typed `current_column_value` slot; an override
  drops its column from the generic-fill advisory (D13). Folded from
  the flat matched path (build_seed_overrides) and applied to the
  per-column plan (apply_seed_overrides).
- `<table>.<column>` column-fill (D1 form 2): an UPDATE over existing
  rows. Refuses PK/autogen targets, empty-table no-op, FK-samples the
  parent, collision-free for UNIQUE/identifier targets, one undo step;
  `set` may only adjust the filled column.

Supporting work: KNOWN_GENERATORS vocabulary + generator_for_name
(src/seed/vocabulary.rs, D9); a range Generator + range_bounds_reason;
IdentSource::Generators and HighlightClass::Function; completion of the
generator vocabulary after `as` and the set/.col column slots; the
typing-time validity indicator for an unknown generator; help,
parse-error pedagogy rows, and the D13 advisory's Phase-2/3 wording.

A bounded override (fixed value / too-short pick-list) on a
single-column-UNIQUE target is a friendly error rather than a silent
uniqueness cap (post-implementation /runda finding, user-chosen).

Dates in the range form are quoted (no date-literal token exists);
ADR-0048 D2 amended accordingly. Both modes (D5); reproducible (D4).

tests/it/parse_error_pedagogy.rs

@@ -110,6 +110,13 @@ fn near_miss_matrix_simple_mode() {
         ("delete from", &["after `delete from`, expected table name", "delete from <Table>"]),
         ("delete from T", &["expected `where` or `--all-rows`", "delete from <Table>"]),
         ("seed", &["after `seed`, expected table name", "seed <Table> [count]"]),
+        // Phase 2 (ADR-0048 D2/D1): malformed `set` clause + column-fill.
+        ("seed T set", &["after `seed T set`, expected column name", "seed <Table>.<col>"]),
+        (
+            "seed T set role",
+            &["after `seed T set role`, expected `=`, `in`, `between`, or `as`", "seed <Table>.<col>"],
+        ),
+        ("seed T.", &["after `seed T.`, expected column name", "seed <Table>.<col>"]),
         ("replay", &["after `replay`, expected string literal or path", "replay <path>"]),
         ("explain", &["after `explain`, expected `show`, `update`, or `delete`", "explain show data"]),
         // advanced-only entry word typed in simple mode → "this is SQL" rail
@@ -540,3 +547,4 @@ fn caret_aligns_under_offending_token() {
 
 
 
+