fix(builder-vite): avoid duplicate publicDir copies with staticDirs

[harshit-d3v]

Summary

• disable Vite's build-time publicDir copy when Storybook staticDirs already includes the same directory
• prevent duplicate root-level asset copies during static builds for Vite-based Storybook projects
• avoid cases where files such as public/index.json can overwrite Storybook's generated storybook-static/index.json
• add regression tests covering default and custom publicDir values, plus build vs development behavior

Closes #24627.

Testing

• yarn vitest run code/builders/builder-vite/src/vite-config.test.ts

Summary by CodeRabbit

• Tests

  • Added test coverage for Vite builder's public directory handling with static directories in build and development modes.

• Bug Fixes

  • Improved Vite builder's public directory configuration based on static directory mappings during production builds.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 0034c793-ce8c-49cc-94b2-224a39da99fa

📥 Commits

Reviewing files that changed from the base of the PR and between aae6c95 and dd73cf4.

📒 Files selected for processing (2)

• code/builders/builder-vite/src/vite-config.test.ts
• code/builders/builder-vite/src/vite-config.ts

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📝 Walkthrough

Walkthrough

These changes add logic to Storybook's Vite builder to conditionally disable Vite's publicDir during production builds when user-defined staticDirs already map to the same resolved directory. Tests verify this behavior across different build modes and configurations.

Changes

Cohort / File(s)	Summary
Core Implementation code/builders/builder-vite/src/vite-config.ts	Adds helper functions to resolve effective publicDir from Vite config and check if staticDirs mappings match it. Sets publicDir: false in build mode when static dir mapping aligns with resolved publicDir.
Test Additions code/builders/builder-vite/src/vite-config.test.ts	Introduces test helpers (createOptions, createTempProject) and four test cases validating commonConfig behavior with publicDir disabled in build mode when staticDirs maps to the same directory, and enabled in other scenarios.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

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