feat: implement billboard monitor support and remove legacy code

inventoryManager.lua

@@ -194,6 +194,15 @@ local function main()
         log.warn("INIT", "No smelter monitor on %s", cfg.SMELTER_MONITOR_SIDE)
     end
 
+    -- Billboard monitor (optional — set billboardMonitorSide in .manager_config)
+    if cfg.BILLBOARD_MONITOR_SIDE ~= "" then
+        if display.setupBillboardMonitor() then
+            log.info("INIT", "Billboard monitor: %s", display.billboardMonName)
+        else
+            log.warn("INIT", "Billboard monitor not found: %s", cfg.BILLBOARD_MONITOR_SIDE)
+        end
+    end
+
     -- Find wired modem for client/turtle communication
     for _, name in ipairs(peripheral.getNames()) do
         if peripheral.getType(name) == "modem" then
@@ -541,6 +550,23 @@ local function main()
             end
         end),
 
+        -- Task 8b: Billboard dashboard redraw (goals monitor)
+        resilient("Billboard", function()
+            if not display.billboardMon then
+                -- No billboard configured, sleep forever
+                while true do sleep(3600) end
+            end
+            state.billboardNeedsRedraw = true
+            while true do
+                if state.billboardNeedsRedraw then
+                    state.billboardNeedsRedraw = false
+                    local bok, berr = pcall(display.drawBillboard)
+                    if not bok then log.error("DRAW", "Billboard: %s", tostring(berr)) end
+                end
+                sleep(0.5)
+            end
+        end),
+
         -- Task 9: Touch event listener (both monitors)
         resilient("Touch-listener", function()
             while true do