fix: Design Tokens naming and escaping a pending token row

[surajshetty3416]

Follow-ups on #676.

• The colour field's action button still read Save as Variable → now Save as Token.
• The panel is called Design Tokens (header and the left sidebar tooltip), not Design System.
• Escape only discarded a pending new row while the name cell had focus, so pressing it from the value cells left an empty row behind. It is handled on the row now, from any cell.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

_{Reviews (2): Last reviewed commit: "fix: hold the token list open on an empt..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.59%. Comparing base (c60696f) to head (9636ba8).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #707   +/-   ##
========================================
  Coverage    59.59%   59.59%           
========================================
  Files           35       35           
  Lines         4413     4413           
========================================
  Hits          2630     2630           
  Misses        1783     1783           

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