feat(hint): advertise the optional seed count in the hint panel (#26)

At `seed <table> ▮` the hint showed only the `set`/`--seed` chips and
never mentioned the optional row count — a bare positional number with no
candidate, on an already-complete command, so neither the candidate
ladder nor the resolver surfaced it. (A prior IntroProse attempt was
reverted: pending_hint_mode is cleared by the trailing optionals.)

Carry a skipped Optional's IntroProse hint: walk_optional stashes the
inner's key into a new WalkContext.surviving_intro_hint (key + position)
before the empty match clears pending_hint_mode; the snapshot keeps it
only when the skip position is the cursor (so it never leaks past a
later-consumed `set …` clause, nor once the count is given); the
resolver returns it ahead of the empty-expected short-circuit. The seed
count is wrapped Hinted{IntroProse("hint.seed_count")}; the prose names
the count (default 20), the `.column` column-fill form, and `set` /
`--seed`. Tab still cycles the keywords.

Only IntroProse is carried; ProseOnly/ForceProse and the CREATE-TABLE
element (a required Repeated) are untouched. No AmbientHint/renderer
change. Fires in both modes.

ADR-0022 Amendment 7; +3 tests.

src/dsl/grammar/data.rs

@@ -438,6 +438,17 @@ const LIMIT_CLAUSE: Node = Node::Seq(LIMIT_CLAUSE_NODES);
 const SEED_COUNT: Node = Node::NumberLit {
     validator: Some(LIMIT_VALIDATOR),
 };
+/// Issue #26: the row count is a bare positional number, so it produces
+/// no Tab candidate and was invisible in the hint panel at
+/// `seed <table> ▮` (only `set` / `--seed` showed). Wrapping it in
+/// `IntroProse` advertises it (and the other options) in prose; the
+/// skipped-optional carry (`surviving_intro_hint`) makes the hint reach
+/// the resolver despite the trailing optionals. Tab still cycles the
+/// keyword candidates.
+const SEED_COUNT_HINTED: Node = Node::Hinted {
+    mode: crate::dsl::grammar::HintMode::IntroProse("hint.seed_count"),
+    inner: &SEED_COUNT,
+};
 /// `--seed <n>` — a reproducible-generation flag carrying a numeric
 /// seed (ADR-0048 D4). The only flag in the DSL that takes a value;
 /// `build_seed` reads the number immediately after the flag.
@@ -567,7 +578,7 @@ const SEED_NODES: &[Node] = &[
     // against this table.
     TABLE_NAME_WRITES,
     SEED_DOT_COLUMN,
-    Node::Optional(&SEED_COUNT),
+    Node::Optional(&SEED_COUNT_HINTED),
     Node::Optional(&SEED_SET_CLAUSE),
     Node::Optional(&SEED_FLAG),
 ];