feat(all theming): Clean and reusable way to override all components theme colors

### Feature Description

Currently, there is a way to generate a custom color palette using the generation tool. However, all components appear too dark regardless of the target color, and there is no single-line solution to specify a base color tone for all components since `--mat-sys-primary` is hardcoded to the tone value `40` by the theme mixin.

Unfortunately, with Material v19, picking colors from the theme no longer works. You can still specify a material theme using `$app-theme: mat.define-theme(...)` with some restrictions, but applying it using the new mixin `@include mat.theme($app-theme)` doesn't work.

**So please provide clean and simple solution to:**

**1. Specify and reuse a theme object**
For example:
```scss
// Define theme object
$app_theme: mat.define-theme((
color: (primary: $primary-palette),
...
)); // Like it was in Material 18

// then use this theme object to apply theme or get theme color:
@include mat.theme($app-theme);
$theme-color: mat.get-theme-color($app-theme, primary, 70);

```
**2. Specify a base color tone for all components at once**
For example:
```scss
@include mat.theme((
color: (
theme-type: light,
primary: themes.$app-theme-palette, // Generated color palette
primary-color-tone: 70 // Here we specify which tone level to pick from color palette for --mat-sys-primary color
...
)
));
```
**_or as an alternative_** output all theme-palette tones as css variables, so we can easily reuse them to customize theme and component colors:
```scss
@include mat.theme-overrides((
primary: var(--mat-sys-primary-70),
on-primary: var(--mat-sys-primary-100)
));

@include mat.autocomplete-overrides((
background-color: var(--mat-sys-primary-80); // or any other custom color
));

```

**3. Specify a base color for a specific component (single-line override)**
For example:
```scss
@include mat.autocomplete-overrides((
base-color: mat.get-theme-color($theme, primary, 30); // or any other custom color
));
```

Comienza revisando los puntos de entrada mencionados mat.define-theme, mat.theme, mat.get-theme-color, mat.theme-overrides y mat.autocomplete-overrides, y cómo gestionan los colores del tema. El issue no menciona archivos ni tests; la implementación final debería proporcionar un objeto de tema reutilizable, tonos base configurables y overrides de color de componentes en una sola línea sin las restricciones descritas.

Escrito por el modelo de indexación a partir del texto del issue.