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/friendly/strings/en-US.yaml

@@ -400,6 +400,12 @@ hint:
   # at `create table T (` so the column-name role is visible
   # alongside the table-level constraint keywords.
   create_table_element: "Type a column name, or a table-level constraint: `primary`, `unique`, `check`, `constraint`, `foreign`"
+  # Issue #26: the `seed <table> ▮` position. The optional row count is
+  # a bare number with no Tab candidate, so it (and the `.column`
+  # column-fill form) would be invisible next to the `set` / `--seed`
+  # chips. Names every option so the most common next move (a count) is
+  # discoverable.
+  seed_count: "Optionally a row count, e.g. `50` (default 20); `.column` to fill one column on existing rows; `set` to pin a column; `--seed` to fix the RNG"
   # Value-literal slot — `insert ... values (`, `update ... set
   # col=`, `where col=`. Replaces the misleading "null true
   # false" keyword candidate list with format guidance for all