test(web): remove Base UI component mocks

[lyzno1]

Summary

• remove the shared fake Popover, DropdownMenu, Select, and Tooltip implementations and their self-test
• keep Dify UI primitives and feature-owned BlockSelector, PluginVersionPicker, and TimePicker wrappers real across Web tests
• rewrite consumers around semantic roles, real portals/state attributes, and user interactions; delete mock-only and unreachable-input tests
• add a source boundary test and testing guidance to prevent interactive component mocks from returning

This is the test-governance follow-up to #39864. It changes no runtime source files.

Scope

• removed 144 direct interactive @langgenius/dify-ui/* mocks
• removed 17 feature-wrapper mocks (11 BlockSelector, 3 PluginVersionPicker, 3 TimePicker)
• net removed 10,063 lines across 130 files

Validation

• 120 affected test files: 1,618 tests passed
• pnpm type-check --pretty false in web/
• pnpm check (0 errors; existing warnings remain)
• git diff --check
• governance scan: 0 target primitive mocks, 0 target wrapper mocks

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.18%. Comparing base (b682433) to head (d5f2a8f).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #39877      +/-   ##
==========================================
- Coverage   86.20%   86.18%   -0.02%     
==========================================
  Files        5088     5088              
  Lines      287759   287759              
  Branches    57329    57329              
==========================================
- Hits       248061   248017      -44     
- Misses      34888    34932      +44     
  Partials     4810     4810              

Flag	Coverage Δ
dify-ui	93.07% <ø> (ø)
web	85.88% <ø> (-0.04%)	⬇️

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