feat: add dify-ui autocomplete and combobox

[lyzno1]

Summary

• add composable Dify UI Autocomplete and Combobox primitives built on Base UI
• document primitive selection and overlay z-index guidance
• include Storybook examples and tests

Starts #35867

Testing

• component tests added and passing
• stories added for visual coverage

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.82%. Comparing base (8fd616d) to head (c4b0390).

Files with missing lines	Patch %	Lines
packages/dify-ui/src/autocomplete/index.tsx	95.00%	3 Missing ⚠️
packages/dify-ui/src/combobox/index.tsx	96.15%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #35868    +/-   ##
========================================
  Coverage   85.82%   85.82%            
========================================
  Files        4458     4460     +2     
  Lines      208954   209092   +138     
  Branches    39071    39112    +41     
========================================
+ Hits       179328   179460   +132     
- Misses      26451    26457     +6     
  Partials     3175     3175            

Flag	Coverage Δ
dify-ui	93.93% <95.65%> (+0.66%)	⬆️
web	86.77% <ø> (ø)

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[CodingOnStar]

LGTM