Fix CSS module digest calculation to use URL paths consistently

[Copilot]

CSS module class names generated by esbuild didn't match Ruby's expectations when using bun. The hash component of class names (e.g., base_0877ac8e_...) differed because Go calculated hashes from file system paths while Ruby used URL paths, and bun installs gems in different locations than traditional bundler.

Changes

Unified hash calculation on URL paths:

• Ruby: Changed from Utils.css_module_digest(abs_path) to Utils.css_module_digest(url_path) where url_path is /node_modules/@rubygems/gem/file.module.css
• Go: Changed from ast.CssLocalHash(args.Path) to ast.CssLocalHash(urlPath) where urlPath follows same format

Aligned path suffix transformation:

• Ruby now matches esbuild's CssLocalAppendice: @ → _, / → -, . → -
• Both sides now produce identical suffixes like node_modules-_rubygems-gem-file-module

Added hash replacement for direct imports:

• Go plugin now replaces old file-path-based hashes in CSS content with new URL-path-based hashes for directly imported CSS modules

Example

Before:

# Ruby generates: base_67482c8c_---hue-app-components...
# Go generates:   base_0877ac8e_node_modules-_rubygems-hue-app-components...

After:

# Both generate:  base_<same-hash>_node_modules-_rubygems-hue-app-components...

Known Limitation

Nested CSS module imports (CSS importing other CSS modules) still contain file-path-based hashes in the CSS content itself. This requires updating the esbuild-internal fork to use URL paths throughout its CSS processing pipeline. Direct imports from JavaScript are fully fixed.

Original prompt

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This section details on the original issue you should resolve

<issue_title>CSS module digest and path incorrect with bun</issue_title>
<issue_description>When using the bun package manager, the resulting CSS module class names do not match those used in Ruby code.

This is in the CSS file:

.base_0877ac8e_node_modules-_rubygems-hue-app-components-icon-component-module # css file

Vs what is in the ruby code:

.base_67482c8c_---hue-app-components-icon-component-module # ruby

Not yet sure which one is correct/incorrect.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes CSS module digest and path incorrect with bun #60

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