refactor(web): use css icons in the tab filter story

[lyzno1]

Summary

• replace two Remix React icons in the TabSliderNew story with the repository's recommended CSS icon classes
• mark the decorative story icons hidden from assistive technology
• remove the two focused icon warnings without touching production code

Scope

Only web/app/components/base/tab-slider-new/index.stories.tsx.

This layer has no production bundle or runtime behavior change.

Visual regression

Compared this story against #40243 with the same viewport and theme.

• both icons remain 16 × 16
• both icons retain the same x/y coordinates, 8 px right margin, and colors
• both item boxes and both text ranges remain unchanged
• the CSS masks use the corresponding Remix icon data recommended by the repository lint rule

Verification

• pnpm exec vp check app/components/base/tab-slider-new/index.stories.tsx — 0 warnings/errors
• pnpm check — 0 errors; repository warning count decreases by 2
• git diff --check

Stack

Base: #40243

This is the final, Storybook-only layer of stack #40245. It can be omitted or reverted without affecting the accessibility fix.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (codex/a11y-tool-category-filter@863bf36). Learn more about missing BASE report.

Additional details and impacted files

@@                        Coverage Diff                         @@
##             codex/a11y-tool-category-filter   #40244   +/-   ##
==================================================================
  Coverage                                   ?   86.41%           
==================================================================
  Files                                      ?     5107           
  Lines                                      ?   290733           
  Branches                                   ?    57916           
==================================================================
  Hits                                       ?   251247           
  Misses                                     ?    34545           
  Partials                                   ?     4941           

Flag	Coverage Δ
dify-ui	93.49% <ø> (?)
web	86.10% <ø> (?)

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[lyzno1]

Closing during the accessibility stack audit. This layer only changes component typing or icon implementation, adds no user-visible accessibility contract, and carries independent visual/review risk. It can be reconsidered later as a separate cleanup, not as an a11y dependency.