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/app.rs

@@ -2097,9 +2097,14 @@ impl App {
             self.note_system(line);
         }
         if !result.advisory_columns.is_empty() {
+            // `column` (the first advised column) seeds the concrete
+            // repair examples (D13 Phase 2/3 wording); `columns` lists
+            // them all.
             self.push_category_three_prose(crate::t!(
                 "seed.advisory_generic",
-                columns = result.advisory_columns.join(", ")
+                columns = result.advisory_columns.join(", "),
+                column = result.advisory_columns[0],
+                table = result.table
             ));
         }
     }
@@ -6268,7 +6273,9 @@ mod tests {
         app.update(AppEvent::DslSeedSucceeded {
             command: Command::Seed {
                 table: "users".to_string(),
+                target_column: None,
                 count: Some(20),
+                overrides: Vec::new(),
                 rng_seed: None,
             },
             result: crate::db::SeedResult {
@@ -6304,7 +6311,9 @@ mod tests {
         app.update(AppEvent::DslSeedSucceeded {
             command: Command::Seed {
                 table: "J".to_string(),
+                target_column: None,
                 count: Some(10),
+                overrides: Vec::new(),
                 rng_seed: None,
             },
             result: crate::db::SeedResult {