feat: add tailwind with toggle theme

[paul58914080]

Checklist:

• My code follows the contribution guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My commits follow conventional commit message guidelines

[Copilot]

Pull request overview

Adds Tailwind CSS v4 styling support and a light/dark theme toggle to the Angular UI, including global design tokens (CSS variables) and an early theme bootstrap to avoid flash-of-incorrect-theme.

Changes:

• Integrated Tailwind via PostCSS and added a Tailwind entrypoint stylesheet.
• Implemented a theme service + toggle component and wired it into the root app shell.
• Updated global styles and HTML lint rules to accommodate Tailwind utility class naming.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
yarn.lock	Adds Tailwind/PostCSS-related dependency resolutions.
package.json	Adds Tailwind + PostCSS dev dependencies.
angular.json	Registers Tailwind stylesheet in the global styles pipeline.
.postcssrc.json	Configures PostCSS to run the Tailwind v4 plugin.
.lint/.htmlhintrc	Disables id-class-value rule to allow Tailwind class naming.
src/tailwind.css	Tailwind entrypoint + custom dark variant + theme tokens.
src/styles.scss	Defines global CSS variables for light/dark palettes and base element styling.
src/index.html	Adds font loading and an early inline script to set the initial theme class.
src/app/core/theme/theme.service.ts	Adds ThemeService to manage theme state, persistence, and DOM class toggling.
src/app/core/theme/theme-toggle.ts	Adds a theme toggle button component with accessible labeling.
src/app/app.ts	Imports the toggle component and wires theme support into the root component.
src/app/app.html	Introduces a basic app shell layout with header, toggle, and router outlet.
src/app/app.scss	Adds app-shell styling (currently unused by the template).

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