remove completed todo items: control panel and About modal

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

todo.md

@@ -143,10 +143,6 @@ When a cell or range is selected, show a compact set of floating action buttons
 
 ## 8. UI & Control Panel
 
-- [ ] **8.1 Implement a compact, functional control panel**
-
-  The current left and bottom panel slots exist but contain only placeholder content. Replace with a small, well-designed panel surfacing the most useful controls. The panel should stay visually aligned with the table as it scrolls (likely `position: sticky` or a scroll event listener).
-
 - [ ] **8.2 Add a "Help" modal**
 
   A small modal (triggered from the control panel) listing and explaining:
@@ -155,10 +151,6 @@ When a cell or range is selected, show a compact set of floating action buttons
   - Keyboard shortcuts
   - How cell references and ranges work
 
-- [ ] **8.3 Replace "About" with a popup modal**
-
-  Remove the current inline disclaimer text. Add an About button that opens a conventional modal with app info, version, and credits.
-
 - [ ] **8.4 Replace the logo**
 
   The current `logo.svg` is a placeholder. Design and replace with a better mark.