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/event_bus.gd

@@ -55,6 +55,8 @@ signal load_finished(slot: StringName, ok: bool, real_seconds_away: int) ## Emit
 # Phase 17 — Touch UX completion.
 signal pawn_selected(pawn)                         ## Emitted when Selection picks a pawn — opens PawnDetailPanel.
 signal pawn_deselected                             ## Emitted when Selection clears — closes PawnDetailPanel.
+signal workbench_selected(workbench)
+signal workbench_deselected
 signal pawn_priority_changed(pawn, category: StringName, level: int) ## Emitted when priority matrix updates a cell.
 signal alert_added(severity: StringName, text: String, focus_tile: Vector2i) ## Emitted by gameplay subsystems to surface a player notice. severity = info | warn | danger.
 signal request_wolf_spawn(count: int)              ## Phase 15 EventCatalog → WolfSpawner. Decouples threat-event effects from spawner.