Spell out "Rectangle" in tool labels instead of "Rect"

Keeps the internal 'rect' annotation type id (canvas/raster/schema)
unchanged; only updates the user-facing toolbar button and shortcuts
help text.

app/renderer/dialogs.js

@@ -649,7 +649,7 @@ const SHORTCUTS = [
     ['Ctrl+V', 'Paste annotation, or clipboard image as new step'],
   ]],
   ['Canvas tools', [
-    ['S R O L A T', 'Select · Rect · Oval · Line · Arrow · Text'],
+    ['S R O L A T', 'Select · Rectangle · Oval · Line · Arrow · Text'],
     ['G N B H M U C', 'Tooltip · Number · Blur · Highlight · Magnify · Cursor · Crop'],
     ['Ctrl+C', 'Copy selected annotation'],
     ['Delete', 'Delete selected annotation'],

app/renderer/editor.js

@@ -189,7 +189,7 @@ class GuideEditor {
     this.root.innerHTML = '';
     const toolButtons = [
       ['select', 'Select'],
-      ['rect', 'Rect'],
+      ['rect', 'Rectangle'],
       ['oval', 'Oval'],
       ['line', 'Line'],
       ['arrow', 'Arrow'],