refactor: simplify public directory path formatting

[chenjiahan]

Summary

Normalize public dir to absolute paths in config normalization phase and reduce redundant path joining logic.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR refactors the public directory path handling by normalizing paths to absolute paths during the config normalization phase, eliminating redundant path resolution logic scattered throughout the codebase.

Key Changes:

• Moved public directory path normalization to the config normalization phase
• Removed path joining logic from middleware, plugin, and HTML processing code
• Added rootPath parameter to normalizeConfig and normalizeConfigStructure functions

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/core/src/defaultConfig.ts	Enhanced normalizePublicDirs to resolve relative paths to absolute paths during config normalization, added validation for empty string paths
packages/core/src/provider/initConfigs.ts	Updated calls to normalizeConfig and normalizeConfigStructure to pass rootPath parameter
packages/core/src/server/devMiddlewares.ts	Removed pwd parameter and path normalization logic, now uses pre-normalized absolute paths
packages/core/src/server/devServer.ts	Removed pwd argument from getDevMiddlewares call
packages/core/src/plugins/server.ts	Removed path normalization logic, uses pre-normalized absolute paths directly
packages/core/src/plugins/html.ts	Simplified favicon path collection by removing redundant path normalization
e2e/cases/html/favicon/index.test.ts	Changed test config from array to object format for publicDir

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