Workbench bill editor — tap a workbench, see/edit bills

Tap-to-select chain extended to workbenches (pawn always wins on shared
tile). Mutually exclusive with pawn selection via EventBus —
selecting one clears the other.

New WorkbenchPanel (scenes/ui/workbench_panel.gd, ~432 LOC, layer 18,
right-anchored 360 px) mirrors PawnDetailPanel shape. Bill rows expose
recipe name, mode (FOREVER / COUNT / UNTIL_N), target count, completed
progress, pause, and remove. Add-bill popup filters RecipeCatalog.all()
by accepted_skill so a Hearth only offers cooking recipes.

Supporting plumbing:
- EventBus.workbench_selected / workbench_deselected signals.
- Workbench.remove_bill() — interrupts mid-craft cleanly via
  on_craft_interrupted() before erasing.
- RecipeCatalog.all() static enumerator + Recipe.display_name() helper.
- World.workbench_at_tile() lookup.
- i18n keys ui.bill.* and ui.workbench.* in strings.gd.

Closes the deferred Phase 17 "Bill UI for workbenches" item. Player-
built workbenches are now functionally configurable; before this
landed, only world.gd-hardcoded bills worked.

autoload/world.gd

@@ -124,6 +124,15 @@ func pawn_at_tile(tile: Vector2i) -> Pawn:
 	return null
 
 
+## Returns the Workbench occupying `tile`, or null if none.  Used by Selection
+## to route taps on a workbench to the bill-editor panel.
+func workbench_at_tile(tile: Vector2i):
+	for w in workbenches:
+		if w.tile == tile:
+			return w
+	return null
+
+
 func clear_pawns() -> void:
 	# For save-load / new-game flow in Phase 16.
 	pawns.clear()