Upgrade build toolchain and fix modern Sass/webpack 5 compatibility

[Copilot]

The build was broken/noisy on modern package versions: 43 Sass deprecation warnings, broken file-loader usage (removed in webpack 5), tilde-prefix imports (~bootstrap) dropped by newer sass-loader, and two npm audit vulnerabilities.

Build config

• fonts.js / images.js: Replace deprecated file-loader with webpack 5 native asset modules (type: 'asset/resource')
• sass.js: Add silenceDeprecations for known Bootstrap 5 + Sass migration warnings (import, global-builtin, color-functions, if-function) — Bootstrap hasn't completed its own @use/@forward migration

SCSS fixes

• _functions.scss, _mixins.scss, _variables.scss, materialize-vendors.scss: Drop ~ prefix on bootstrap/scss/ imports
• _base.scss: Fix loop iterating $theme-colors (flat map) as if it were nested — replace with $theme-palette (nested main/dark/light map); fix Sass color-in-interpolation warning using '' + $value

Dependencies (package.json / package-lock.json)

• Remove unused url-loader
• Restore accidentally missing webpack ^5.98.0 explicit devDependency
• npm audit fix: resolves cross-spawn (high) and ajv (moderate) → 0 vulnerabilities

Net result: webpack 5.105.3 compiled successfully with 0 warnings, down from 43.

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