add iron/gold smelting + disambiguate workbench-vs-recipe

Q: iron_smelt (iron_ore + wood → iron_ingot) and gold_smelt
(gold + wood → gold_ingot) recipes added at Smelter, using the
existing ingredient2 buffer mechanism. New TYPE_IRON_INGOT and
TYPE_GOLD_INGOT item types (procedural hue-hash draw for now).

R: new Recipe.target_workbench field (StringName, empty = any matching
skill) round-trips through to_dict/from_dict. Workbench bill picker
filters by both required_skill AND target_workbench vs lower-cased
label_text. plank → carpenter, stone_block/iron_smelt/gold_smelt →
smelter, flour → millstone. Cooking-only recipes (bread, meal) stay
unrestricted since Hearth is the only cooking workbench.

9 recipes total now, 4 distinct workbench routes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

autoload/strings.gd

@@ -39,6 +39,9 @@ const TABLE: Dictionary = {
 	# Phase 6 — new item types (carpenter bench + smelter outputs)
 	&"item.plank":       "Plank",
 	&"item.stone_block": "Stone block",
+	# Phase 19 — smelted ingots
+	&"item.iron_ingot":  "Iron ingot",
+	&"item.gold_ingot":  "Gold ingot",
 	# Phase 7 — food loop and cooking chain item types
 	&"item.flour":          "Flour",
 	&"item.bread":          "Bread",