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).

src/input_render.rs

@@ -817,6 +817,9 @@ fn ambient_hint_core_in_mode(
             crate::dsl::grammar::IdentSource::Tables => "table",
             crate::dsl::grammar::IdentSource::Columns => "column",
             crate::dsl::grammar::IdentSource::Relationships => "relationship",
+            // The `seed … set <col> as <gen>` curated vocabulary
+            // (ADR-0048 D9) flags an unknown name here.
+            crate::dsl::grammar::IdentSource::Generators => "generator",
             // `NewName`, `Types`, `Free` are filtered out by
             // `invalid_ident_at_cursor` (it only fires for
             // known-set sources via `completes_from_schema`), so