feat(lang): 27.3 - a reducer on a table's row: reducer T in S.table on A, @Target, Row<T>, @RowVerb, @Column

An action names one row of a ludic.base Table<T> by its handle, in a field marked @Target, and
`reducer Deer in Herd.deer on Spook(r: mut Row<Deer>, n: Noise, a: Spook)` runs once, for that row
alone (the table may sit down a path, S.w.tab). The drain resolves the handle (tb_row) and hands the
reducer a Row<T> - new in ludic.base: tb, row, h, rec - that the queue keeps, one per row reducer,
filled in place, so a targeted action allocates nothing; a stale handle runs nothing, and
LUDIC_ACTIONS_LOG=1 prints a line for it (@alloc_ok). Row reducers order among an action's by their
state's name, then the table's path.

Checked at compile time (actions_rows.ludic): the row reaches r.rec and r.h only - r.tb / r.row
refused, the view never assigned, stored, copied or handed on except to a @RowVerb (a function of
the record's own module taking Row<T> first; any other function taking a row is refused); a field
marked @Column (a table column mirrors it) is not written through r.rec; only the module owning the
state declares a row reducer; one @Target, an int, per action; the states between the row and the
action are read. `mut` is allowed on a Row<T> parameter.

ludic schema's code section gains row_reducers (record, table, state, action, target, predicted,
net, module, at) and row_verbs (name, record, module, at), and every action its target; row
reducers are left out of `reducers`. ludic deps and ludic-lsp name a row reducer
`reducer Deer in Herd.deer on Spook`. vocab: @Target, @Column, @RowVerb; docs/language pages;
LANGUAGE.md "A reducer on a row"; examples actions/rows and ten rejects; test.ludic feat, reject and
schema cases (not run); changes/row-reducers.md. Reseeded; bootstrap-cfree fixpoint holds (307497
lines); Maroon Lake's `ludic build --check` is clean against this tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/backend/emit_vis.ludic

@@ -48,7 +48,7 @@ function vis_check(d: Node, what0: pointer) -> void {
   # 0.S/0.R: a state's instance, the action queue and a reducer are the runtime's to supply and to
   # call - the code that names them depends on no module for it
   if d.kind == N_VAR and d.uns == 1 and str_prefix(d.s, "state$") and is_state_ty(d.ty) { return }
-  if d.kind == N_FN and (str_prefix(d.s, "ludic_reduce__") or is_action_builtin(d.s)) { return }
+  if d.kind == N_FN and (str_prefix(d.s, "ludic_reduce__") or str_prefix(d.s, "ludic_rowred__") or is_action_builtin(d.s)) { return }
   deps_edge(d, what0)                            # LUDIC_DEPS: the graph ludic deps reads (emit_deps.ludic)
   if g_vis_off { return }
   if d.file == null { return }