Refactor styles to CSS

[SharonStrats]

Ticket SolidOS/solidos#244

This has been tested in solid-panes linking to my local folder-pane on this branch.

[Copilot]

Pull request overview

This PR refactors folderPane styling from inline styles to dedicated CSS files and updates the build setup to accommodate CSS assets.

Changes:

• Move inline styling in src/folderPane.ts to new CSS files under src/styles/ and import them from the pane entrypoint.
• Add a production webpack config that emits UMD bundles and copies src/styles into lib/styles.
• Update TS/CSS typing and package metadata to support CSS imports.

Reviewed changes

Copilot reviewed 6 out of 9 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
webpack.config.mjs	Adds a production build that outputs folder-pane(.min).js and copies CSS assets.
webpack.module.rules.mjs	(Context) Confirms .css is global/side-effect and .module.css uses CSS modules.
package.json	Switches to ESM package mode, updates main, and marks CSS as side-effectful; adds webpack-related deps.
package-lock.json	Locks new dependencies and related transitive updates.
tsconfig.json	Includes declarations.d.ts so TS accepts CSS imports during local builds.
declarations.d.ts	Adds a TS module declaration for *.css imports.
src/folderPane.ts	Replaces inline styles with CSS class usage and imports the new CSS.
src/styles/folderPane.css	Introduces pane-specific class styles.
src/styles/utilities.css	Adds shared CSS variables (e.g., icon sizing).
dev/index.js	Adjusts imports for the dev harness to include extensions.

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