Fix renderer scope collisions, editor bugs; add welcome screen

Bug fixes from code review:
- Wrap renderer modules (canvas/dialogs/editor/app) in IIFEs: duplicate
  top-level 'const api' across plain scripts threw a SyntaxError that
  prevented app.js from ever running (blank window), and dialogs.js/
  editor.js silently overrode each other's labeledRow/makeSelect
- Focused-view toggle now writes step.focusedView.enabled instead of a
  nonexistent flat field that the schema dropped on save
- Annotation property edits no longer rebuild the panel on every
  keystroke (focus was stolen mid-typing); debounced save instead
- flushStep/undo/redo keep this.steps in sync with stepMap so the step
  list stops going stale after the first save
- Escape now deselects the annotation; Delete remains the delete key

Welcome screen (per spec): app opens to a title at top and three
buttons at the bottom — New Capture (creates a guide, opens the editor,
starts a capture session), Existing Workspace (library), Settings.
Brand click returns to the welcome screen.

Adds an env-gated dev screenshot hook (STEPFORGE_SCREENSHOT[_JS]) used
to visually verify welcome/library/editor views under WSLg.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/main.js

@@ -76,7 +76,29 @@ function createWindow() {
     },
   });
   mainWindow.loadFile(path.join(__dirname, 'renderer', 'index.html'));
-  mainWindow.once('ready-to-show', () => mainWindow.show());
+  mainWindow.once('ready-to-show', () => {
+    mainWindow.show();
+    // Dev-only verification hook: optionally navigate, then write a
+    // screenshot locally and exit. Used by the smoke tooling.
+    if (process.env.STEPFORGE_SCREENSHOT) {
+      const target = process.env.STEPFORGE_SCREENSHOT;
+      const navigate = process.env.STEPFORGE_SCREENSHOT_JS || '';
+      setTimeout(async () => {
+        try {
+          if (navigate) {
+            await mainWindow.webContents.executeJavaScript(navigate, true);
+            await new Promise((r) => setTimeout(r, 900));
+          }
+          const image = await mainWindow.webContents.capturePage();
+          fs.writeFileSync(target, image.toPNG());
+        } catch (err) {
+          console.error('screenshot failed:', err.message);
+        } finally {
+          app.quit();
+        }
+      }, 1500);
+    }
+  });
   mainWindow.on('closed', () => { mainWindow = null; });
 }