fix: type colors into the Background field and keep its label in sync

[surajshetty3416]

Follow-ups to #813 for the Background field.

• Text selects on focus, for Background and Text Color. Autocomplete gains selectOnFocus; select() is skipped when a popover already took the focus on that same focus, since it would hand it back and toggle the popover shut.
• Typed colors apply. A hex (with or without #), rgb, hsl or image path typed into the field sets the background; anything else is ignored and the label restored. parseBackground decides what a value means, for the base value and for state variants, while the "copy current value to state" path still copies the real base styles.
• The label follows the popup. Autocomplete skipped syncing its text while its list was open, and the list never closed once the picker popover took the focus, so a color picked there left "Gradient" in the field. Model changes now always sync the text; only option refreshes wait for the list to close.

[greptile-apps]

Confidence Score: 5/5

Safe to merge; the previous malformed-color issue is fixed and resolved, with no new actionable findings.

_{Reviews (3) · Last reviewed commit: "chore: trim comments around the Backgrou..."}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.89%. Comparing base (acc4c1b) to head (f7211b6).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #816   +/-   ##
========================================
  Coverage    66.89%   66.89%           
========================================
  Files           94       94           
  Lines        10505    10505           
========================================
  Hits          7027     7027           
  Misses        3478     3478           

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