feat: replace browser dialogs with in-game naming screen + notifications

Remove prompt() and alert() calls that broke game immersion. Add:
- Pokemon-style naming screen with character grid + direct typing
- Canvas-rendered notification toasts (with fade-out animation)
- Both render on top of workshop AND world mode canvases
- Workshop keyboard handler yields to naming screen when active

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

js/world/worldInput.js

@@ -2,7 +2,7 @@
 import { worldState, advanceDialog, startDialog } from './worldState.js';
 import { getMap, getInteraction, getNPC, getExit, isWalkable } from './maps.js';
 import { toggleDebug } from './worldRenderer.js';
-import { isBackpackOpen, openBackpack, handleBackpackInput } from './inventory.js';
+import { isBackpackOpen, openBackpack, handleBackpackInput, isNamingActive, handleNamingInput } from './inventory.js';
 
 const keysDown = new Set();
 let interactionHandler = null;
@@ -26,6 +26,13 @@ function onKeyDown(e) {
     const key = e.key;
     keysDown.add(key);
 
+    // Naming screen — route all input there
+    if (isNamingActive()) {
+        e.preventDefault();
+        handleNamingInput(key);
+        return;
+    }
+
     // Backpack open — route all input there
     if (isBackpackOpen()) {
         e.preventDefault();