refactor(Variables): Use UUID for variable ids

[surajshetty3416]

• Remove default grays since those are useless
• Use UUID for variable ids so that variable names can be rename even after using them without have to worry about loosing reference
• Add option to toggle page theme from canvas. Basically detached it from editor's theme. You no longer have to switch your entire editor's theme just to check page in different mode.

Screen.Recording.2026-06-04.at.6.39.41.PM.mov

• Bust cache once the variable value is changed
• Added option to group variables

Before	After

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.54%. Comparing base (e681430) to head (6546e85).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ilder/doctype/builder_variable/builder_variable.py	0.00%	16 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #622      +/-   ##
===========================================
- Coverage    58.56%   58.54%   -0.02%     
===========================================
  Files           29       29              
  Lines         3282     3288       +6     
===========================================
+ Hits          1922     1925       +3     
- Misses        1360     1363       +3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.